Quad O is the shorthand oil and gas operators use for the EPA's OOOO family of air rules, which limit methane and volatile organic compound emissions from the industry. The letters are literally four O's, hence Quad O, and the rules have grown into a lettered series that now drives leak surveys, equipment standards, and monitoring across the sector. This guide explains what Quad O is and where it fits.
EPA Quad O / OOOO in one line: EPA Quad O refers to Subpart OOOO of the New Source Performance Standards (40 CFR Part 60) for the oil and natural gas sector, along with its successors OOOOa, OOOOb, and OOOOc. These rules limit methane and VOC emissions from wells, storage tanks, compressors, pneumatic devices, and other equipment, and they require leak detection and repair (LDAR) programs to find and fix fugitive emissions.
Quad O is the informal name for the EPA's New Source Performance Standards for the crude oil and natural gas source category, codified as Subpart OOOO of 40 CFR Part 60. The 'quad O' nickname simply reflects the four O's in the subpart designation. The original OOOO rule targeted VOC emissions from newly built and modified sources; later subparts expanded the scope to methane, a potent greenhouse gas.
The family now includes several subparts. OOOO and OOOOa apply to sources constructed or modified after specific dates and set standards for equipment and work practices. OOOOb sets standards for new and modified sources going forward, and OOOOc directs states to develop plans covering existing sources, which is a significant expansion because it reaches equipment already in the field.
Quad O rules combine equipment standards with work-practice standards. Equipment standards cover specific emission sources such as storage vessels, controllers, compressors, and completions, often requiring emission controls or low-bleed and zero-bleed equipment. Work-practice standards center on leak detection and repair: operators must survey sites on a defined frequency using approved methods, then repair leaks within set timeframes.
Monitoring methods have modernized alongside the rules. Traditional optical gas imaging cameras and Method 21 instrument surveys are being supplemented by advanced approaches, including continuous monitoring systems and periodic screening, reflecting the EPA's push toward faster detection of large emission events. The rules require recordkeeping and reporting that documents surveys, leaks found, and repairs completed.
Quad O touches almost every surface facility in upstream and midstream oil and gas: well pads, tank batteries, compressor stations, and gathering infrastructure. For operators it means recurring leak surveys, controlled or eliminated venting from tanks and pneumatics, and a growing emphasis on demonstrating that emission controls actually work over time.
It sits alongside, not inside, the safety and pipeline frameworks. Where PHMSA governs pipeline safety and OSHA governs worker safety, Quad O is an environmental air rule enforced by the EPA, frequently implemented in coordination with state agencies such as the TCEQ in Texas. Because compliance now leans heavily on continuous and frequent monitoring, the data side of emissions has become an operations discipline, not just a periodic paperwork exercise.
They are successive subparts with different applicability dates and scopes. OOOO and OOOOa apply to sources constructed or modified after specific past dates, with OOOOa adding methane coverage. OOOOb sets standards for new and modified sources going forward, and OOOOc is an emission guideline directing states to write plans covering existing sources. OOOOc matters most because it reaches equipment already operating in the field, not just new builds.
LDAR stands for Leak Detection and Repair. Under Quad O, operators must survey facilities on a defined schedule using approved methods such as optical gas imaging or EPA Method 21 instrument monitoring, identify components that are leaking, and repair them within specified timeframes. The program is documented with recordkeeping that shows what was surveyed, what leaked, and when it was fixed, and monitoring is increasingly moving toward continuous systems.
Quad O compliance depends on documenting surveys, leaks, repairs, and, increasingly, continuous emissions data. A SCADA and monitoring platform such as Merobix can ingest and time-stamp data from field instruments and emissions monitors over standard protocols like Modbus, DNP3, and MQTT, giving operators a centralized, auditable record. The regulatory determination remains the operator's responsibility, but centralized data makes the recordkeeping and trend analysis far easier.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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