The EPA’s New Source Performance Standards (NSPS) Subparts OOOOa and OOOOb regulate methane and volatile organic compound (VOC) emissions from the oil and natural gas industry. Subpart OOOOa applies to sources that commenced construction, modification, or reconstruction after September 18, 2015, through December 6, 2022. Subpart OOOOb, finalized in the March 2024 rule, applies to sources after December 6, 2022, and introduces more stringent requirements for fugitive emissions monitoring, storage vessels, pneumatic controllers, and control devices. Because most oil and gas facilities have equipment subject to both subparts, a comprehensive program audit should evaluate compliance with both OOOOa and OOOOb requirements across all affected source categories. This audit checklist covers applicability determinations, LDAR programs, storage vessel controls, pneumatic controllers, compressors, well completions, control devices, and annual reporting through EPA’s Compliance and Emissions Data Reporting Interface (CEDRI).
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Download Checklist (.docx)Regulatory Requirements
40 CFR 60, Subpart OOOOa — Standards of Performance for Crude Oil and Natural Gas Facilities (2016)
Subpart OOOOa established NSPS for methane and VOC emissions from oil and gas sources that commenced construction, modification, or reconstruction after September 18, 2015. Key requirements include semiannual OGI-based LDAR surveys at well sites and compressor stations, emission controls for storage vessels exceeding 6 tpy VOC, low-bleed pneumatic controller requirements, green completion requirements for hydraulically fractured wells, and semiannual reporting through CEDRI.
40 CFR 60, Subpart OOOOb — Standards of Performance for Crude Oil and Natural Gas Facilities (2024)
Subpart OOOOb applies to sources commencing construction, modification, or reconstruction after December 6, 2022. It strengthens requirements with tiered LDAR frequencies based on facility type, mandatory AVO inspections between OGI surveys, zero-emission pneumatic controller requirements, 95% emission reduction for storage vessels (methane and VOC), phase-out of routine flaring, enhanced control device monitoring including NHV requirements, and the Super-Emitter Response Program.
Clean Air Act Sections 111(b) and 111(d)
NSPS OOOOa and OOOOb are promulgated under CAA Section 111(b), which authorizes EPA to establish standards of performance for new stationary sources. Section 111(d) provides authority for Emission Guidelines (EG OOOOc) that states use to develop plans for existing sources. Facilities must comply with the applicable subpart based on when construction, modification, or reconstruction commenced.
Regulatory note: Although the Trump Administration announced plans to reconsider OOOOb/c in March 2025, the rule remains in effect and enforceable. EPA extended certain compliance deadlines in November 2025 for control devices, equipment leaks, storage vessels, process controllers, and covers/closed vent systems. However, core requirements including fugitive emissions monitoring at well sites and compressor stations, and annual reporting through CEDRI, remain unchanged. Facilities should maintain compliance programs while monitoring for any future regulatory changes.
Program Documentation and Applicability
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Applicability determination | Facility has documented which subpart (OOOOa or OOOOb) applies to each affected source category based on construction, modification, or reconstruction date. Sources constructed/modified after September 18, 2015 through December 6, 2022 are under OOOOa; after December 6, 2022 under OOOOb. |
| Affected facility inventory | Complete inventory of all affected facilities including well sites, centralized production facilities, compressor stations, storage vessels, pneumatic controllers, pneumatic pumps, and process equipment. Each entry identifies applicable subpart and affected facility status. |
| EPA ID and registration | Facility is properly registered with EPA. Notifications have been submitted as required per 40 CFR 60.5420a or 60.5420b within the required timeframes (60 days of initial startup for OOOOa; per applicable provisions for OOOOb). |
| Written compliance program | Documented compliance program covers all affected sources and applicable requirements. Program identifies responsible personnel, monitoring schedules, recordkeeping procedures, and reporting deadlines. Program is accessible to all operating personnel. |
| Modification tracking | Process exists to evaluate whether physical or operational changes constitute a modification triggering OOOOb applicability. Modification determinations are documented and retained. Threshold criteria (e.g., emissions increase, process change) are understood by operations staff. |
Fugitive Emissions and LDAR Program
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| LDAR program coverage | All fugitive emissions components at affected well sites, centralized production facilities, and compressor stations are included in the monitoring program. Component inventory is maintained and updated as equipment changes. Exempt sources are properly documented. |
| OGI survey frequency | OGI surveys are conducted at required frequency. OOOOa: semiannual for well sites and compressor stations. OOOOb: tiered based on facility type — semiannual for multi-wellhead sites, quarterly for compressor stations, with biennial available for demonstrated low-emitting sites. Survey due dates are tracked and met. |
| AVO inspections | Audible, visual, and olfactory (AVO) inspections are conducted at required intervals between OGI surveys. OOOOb requires quarterly AVO for single wellhead-only sites and between OGI surveys for other facility types. AVO findings are documented and follow-up actions recorded. |
| OGI camera operation | OGI equipment meets specifications per 40 CFR 60, Appendix K (OOOOb) or 60.5397a (OOOOa). Camera operators have completed required training. Daily instrument functionality checks are documented. OGI survey parameters (wind speed, ambient temperature, viewing distance) are recorded. |
| Leak repair tracking | Identified leaks are tagged, photographed (digital photo with date and location), and documented immediately upon discovery. Repairs are initiated within required timeframes (30 days for OOOOa/OOOOb multi-well sites, 15 days for OOOOb single-well sites). Repair completion is verified by follow-up OGI within required period. |
| Delay of repair documentation | Any repair delays beyond the initial repair period are properly documented with technical justification. Delayed repairs are tracked to next shutdown or turnaround opportunity or within two years of detection, whichever is sooner. Delay of repair inventory is maintained and reviewed. |
| Monitoring plan | Written monitoring plan defines the monitoring path, component identification methodology, and procedures for conducting OGI and AVO surveys at each facility. Plan addresses site-specific conditions including difficult-to-monitor and unsafe-to-monitor components. |
Storage Vessels
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Emissions determination | Potential VOC and methane emissions are calculated for each storage vessel or tank battery using accepted methodology. OOOOa threshold: ≥6 tpy VOC. OOOOb threshold: ≥6 tpy VOC or ≥20 tpy methane (based on aggregate tank battery emissions). Calculations are documented and retained. |
| Control requirements | Storage vessels exceeding applicable thresholds achieve required emission reduction: 95% for both OOOOa and OOOOb. Control devices (vapor recovery units, enclosed combustors, flares) are properly sized, installed, and operational. Continuous compliance is demonstrated. |
| Tank battery definition | OOOOb defines storage vessel affected facilities based on aggregate tank battery emissions (not individual vessels). Tank battery groupings are properly determined. All storage vessels in a battery sharing manifolded vapor space are included in the emissions calculation. |
| Low-production exemption | Where applicable, facilities claiming the low-production exemption have demonstrated uncontrolled actual VOC emissions below 4 tpy and methane below 14 tpy for 12 consecutive months. Monthly monitoring records support the exemption. Re-evaluation trigger criteria are understood. |
| Closed vent system integrity | Closed vent systems routing storage vessel vapors to control devices are inspected per required schedule. Systems are designed and operated with no detectable emissions. Initial and ongoing inspections verify no leaks. Defects identified during inspections are repaired within required timeframes. |
Pneumatic Controllers and Pumps
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Controller inventory | All pneumatic controllers are inventoried with type (continuous bleed, intermittent, zero-emission), bleed rate, and applicable subpart. Location of each controller is documented. |
| OOOOa compliance | Pneumatic controllers at OOOOa-affected facilities operate with a bleed rate ≤6 scfh (natural gas processing plants) or are low-bleed. High-bleed controllers have been replaced or retrofitted. Functional necessity documentation exists for any controllers exceeding the bleed rate limit. |
| OOOOb zero-emission requirement | Pneumatic controllers constructed/modified after December 6, 2022 are non-emitting (air-driven, electric, or routed to a closed vent system and control device). Zero-emission conversion or installation is documented. Any exemptions for technical infeasibility are properly justified and documented. |
| Pneumatic pump compliance | Pneumatic pumps at affected facilities meet applicable emission reduction requirements. OOOOa: 95% reduction for pumps at processing plants. OOOOb: applicable reduction requirements for pumps based on facility type. Natural gas-driven diaphragm pumps are evaluated and controlled as required. |
Compressors
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Reciprocating compressor compliance | Reciprocating compressors replace rod packing before exceeding 26,000 hours of operation or 36 months since last replacement, or route emissions to a process or control device. Operating hour meters or replacement schedules are maintained and documented. |
| Centrifugal compressor compliance | Centrifugal compressors with wet seal systems reduce emissions by 95% using a control device or route emissions to a process. Dry seal centrifugal compressors are exempt from control requirements but must be documented as dry seal. |
| Compressor station LDAR | Compressor stations are included in the fugitive emissions monitoring program at required frequency. OOOOa: semiannual OGI. OOOOb: quarterly OGI for gathering and boosting and transmission and storage compressor stations. All fugitive emission components within the station boundary are surveyed. |
Well Completions and Associated Gas
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Green completion requirements | Hydraulically fractured or refractured oil and gas wells use reduced emission (green) completions. Completion combustion devices capture or combust all flowback gas not sent to the sales line. Pit flaring during completions meets all applicable requirements. |
| Associated gas management (OOOOb) | OOOOb facilities comply with the phase-out of routine flaring of associated gas from new oil wells. Associated gas is captured, routed to sales, reinjected, or used on-site. Flaring allowance periods and volume limits are tracked and documented per the transition schedule. |
| Completion records | Well completion reports document dates, duration, gas volumes captured and flared, equipment used, and compliance method. Records are maintained for each completion event and retained for the required period. |
Control Devices and Combustion
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Flare requirements | Flares used for emission control meet design and operational requirements. Pilot flame is continuously maintained with monitoring (thermocouple or equivalent). OOOOb: flares comply with net heating value of combustion zone (NHVcz) monitoring requirements. Visible emissions are minimized. |
| Enclosed combustion devices | Enclosed combustion devices (vapor combustors, thermal oxidizers) achieve required destruction efficiency (≥95% for VOC/methane). Performance tests are conducted per required schedule. Continuous monitoring of operational parameters is maintained. |
| Vapor recovery units | Vapor recovery units (VRUs) achieve required capture and control efficiency. VRU operational uptime is tracked and downtime events are documented. Back-up control (flare or enclosed combustor) is available during VRU downtime. |
| Covers and closed vent systems | All covers on storage vessels, separators, and other controlled equipment are maintained in good condition. Closed vent systems are designed to operate with no detectable emissions. Bypass devices are equipped with a flow indicator, seal, or equivalent. Inspections verify no visible gaps, cracks, or openings. |
Reporting and Recordkeeping
| Audit Item | Expected Finding / What to Evaluate |
|---|---|
| Annual report submission | Annual reports are submitted through EPA’s Compliance and Emissions Data Reporting Interface (CEDRI) within required timeframe. OOOOa: semiannual reports. OOOOb: annual reports due within 90 days after each compliance period. Report covers all affected facilities and all applicable requirements. |
| LDAR records completeness | Records include date, operator, instrument information, and findings for each OGI and AVO survey. Leak detection records include component identification, digital photograph, date found, date repaired, and verification method. Records are retained for the required period (at least 5 years). |
| Equipment-specific records | Maintenance and compliance records are maintained for each affected source category: compressor rod packing replacement dates and hours, storage vessel emissions calculations, pneumatic controller inventories, and well completion reports. Records support compliance demonstrations. |
| Deviation reporting | Deviations from any applicable requirement are documented and reported in the annual report. Malfunctions and corrective actions are logged. Prompt notification requirements (e.g., excess emissions during startup/shutdown/malfunction) are understood and followed. |
| Super-Emitter Response Program | Facility has procedures for receiving and responding to EPA Super-Emitter Event notifications. Investigation must be initiated within 5 calendar days of notification. Response includes review of monitoring data and investigation of potential sources. Findings are documented and reported to EPA within required timeframe. |
Tip: Many facilities have equipment subject to both OOOOa and OOOOb. Track each piece of equipment’s construction/modification date to determine which subpart applies. Sources constructed before December 6, 2022 remain subject to OOOOa; sources after that date fall under OOOOb.
Corrective Actions
Common Issues and Responses
- Missing applicability determination: Conduct a comprehensive review of all equipment and operations to determine which subpart applies to each source. Document construction, modification, and reconstruction dates. Create a master compliance matrix.
- Overdue OGI surveys: Schedule immediate OGI surveys for any facilities past their monitoring deadline. Ensure OGI technicians are trained and equipment is calibrated. Document the late survey as a deviation in the next annual report.
- Unrepaired leaks beyond deadline: Expedite leak repairs and verify completion with follow-up OGI. Document the delay with technical justification. Report overdue repairs as deviations. Implement a tracking system to prevent recurrence.
- Non-compliant pneumatic controllers: Inventory all non-compliant controllers and develop a replacement/conversion plan. Prioritize high-bleed controllers for immediate replacement. Budget for conversion to instrument air or electric actuation at OOOOb-affected facilities.
- Storage vessel emissions exceeding threshold: Install or verify operation of control equipment to achieve 95% reduction. Recalculate potential emissions with current production data. Consider operational changes (e.g., separator optimization) to reduce tank loading rates.
- Missing or late CEDRI reports: Prepare and submit overdue reports immediately through CEDRI. Implement calendar reminders for future reporting deadlines. Assign report preparation responsibilities to specific personnel with backup coverage.
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