Midstream operators had been watching the rulemaking calendar for two years. The EPA's finalization of 40 CFR Part 60, Subpart OOOOb in March 2024 answered several questions that had been left open by the 2022 supplemental proposal. But it also introduced new obligations that operators are still mapping to their site portfolios heading into the second half of 2026. Here is where the compliance calendar currently stands and what the near-term obligations actually mean for gathering and compression operations.
What Changed from OOOOa to OOOOb
OOOOb builds on the OOOOa framework but expands its scope in meaningful ways. The most significant structural change is the addition of a superemitter response program, which creates a new trigger for corrective action that comes from outside your own monitoring program. Under OOOOa, your LDAR schedule and your detection equipment defined your compliance posture. Under OOOOb, a third-party aerial survey, a satellite detection report, or a community monitoring sensor can notify EPA of an event at your site, and the clock starts running whether you knew about it or not.
The continuous emissions monitoring requirement also got sharper in OOOOb. For well sites above a defined well count threshold, operators must deploy either a continuous monitoring system or conduct quarterly OGI surveys. Compressor stations at gathering facilities fall under a separate monitoring frequency requirement. The rule distinguishes between different equipment types: reciprocating compressor rod packing, centrifugal compressor wet seal systems, and pneumatic controllers each have their own monitoring and control obligations.
The Compliance Calendar for 2026
The phased compliance structure of OOOOb means that different provisions came into force at different times. By January 2025, operators were required to have completed initial equipment inventories for affected sources at well sites with more than three wells. The monitoring method selection, whether OGI, continuous optical gas imaging, or point sensor arrays, was supposed to be locked in before the first quarterly monitoring period of 2025.
For 2026, the critical milestones fall into three buckets.
Repair Timelines and Verification
Once a leak is detected under OOOOb, the repair window has been tightened relative to OOOOa. For most components, operators have 30 days to attempt first repair and 60 days for verified repair. The repair attempt must be documented with date, method used, and result. Verified repair requires a follow-up monitoring survey, not just a visual inspection. This is where continuous monitoring changes the workflow: rather than scheduling a follow-up OGI survey weeks later, a system that never stops monitoring can confirm repair within hours of the crew completing the job.
Recordkeeping and Electronic Reporting
OOOOb expanded the electronic recordkeeping requirements. Operators must retain monitoring data, repair records, and test results for five years and be prepared to produce them during an inspection. The EPA has been more aggressive in data requests since OOOOb took effect. If your monitoring data lives in a spreadsheet maintained manually by one EHS coordinator, the practical burden of a data request is significant. The format and completeness of that record matters as much as whether the monitoring was conducted at all.
Superemitter Response Timelines
This is the provision that most midstream operators underestimated in the first year of OOOOb. When EPA receives notification of a potential superemitter event, the operator has five days to acknowledge receipt and 15 days to submit an initial investigation report. The five-day window runs from the date of notification, not from the date you happened to check your email. If your operations team has not set up an alert workflow tied to EPA's notification system, you may find out about a violation after the initial deadline has passed.
What the Rule Does Not Cover
A common point of confusion involves the boundary between new and modified sources under NSPS and existing sources under the separate EG (Emission Guidelines) framework. OOOOb applies to equipment constructed, modified, or reconstructed after December 6, 2022. Equipment that was in service before that date falls under different regulatory tracks, including the OOOOc EG framework that applies to existing sources. Operators who assumed OOOOb applied across their entire asset base may have been doing compliance work for equipment that is actually governed by state plans under the EG framework.
This is a critical distinction. We see operators treating OOOOb as their universal compliance framework, when in reality a large fraction of their compressor stations may predate the applicability cutoff. Understanding which assets are subject to which regulatory track affects both the monitoring frequency you are obligated to maintain and the repair timelines that apply.
How Continuous Monitoring Maps to OOOOb
The rule explicitly contemplates continuous monitoring as an alternative to quarterly OGI surveys for affected well sites. The technical specification for an approved continuous monitoring system requires detection capability for methane concentrations at or above defined levels, with instrument response times fast enough to detect and flag exceedances in real time. It also requires periodic instrument calibration with documented calibration records.
What continuous monitoring does not do, by itself, is satisfy every OOOOb obligation. You still need a documented corrective action process, records of all detected events and their disposition, and a plan for responding to third-party superemitter notifications. Continuous monitoring accelerates the detection side of that workflow, but the documentation and response procedures are still the operator's responsibility to build and maintain.
What to Get Right Before Q4 2026
Three things have come up repeatedly in conversations with operators working through OOOOb implementation. First, the equipment inventory is often the weakest link. If you do not have a current, accurate list of all components subject to OOOOb at each affected site, the rest of the compliance program is built on a shaky foundation. Second, the repair verification workflow needs to be written down, not just understood by the EHS team. When an EPA inspector asks how your team confirms that a repair is complete, a verbal answer is not enough. Third, the superemitter notification response process needs to be tested. Run a drill where you receive a simulated superemitter notification and trace the response through your organization to verify that someone can meet the five-day acknowledgment deadline without heroic effort.
The operators who are in the best position heading into 2026 enforcement activity are the ones who treated OOOOb as an operational change, not just a compliance filing exercise. The rule created new timelines, new data obligations, and a new external trigger that can start the clock on corrective action. The monitoring technology is one piece of the compliance picture, but the workflow, documentation, and notification systems are where enforcement risk concentrates.
Note: This article reflects our reading of publicly available regulatory text and EPA guidance documents. It does not constitute legal or compliance counsel. Confirm applicability, timelines, and specific obligations with qualified environmental counsel and your state regulatory contacts before making compliance decisions.