Williams (WMB) has started service on an expansion of its MountainWest Overthrust Pipeline (MWOP). The project is one of several planned on WMB systems to boost gas flows from the eastern Rockies to markets in the West.
Williams started service on the Westbound Compression expansion in 4Q25, increasing firm capacity by ~325 MMcf/d. The project adds compression at the Rock Springs and Point of Rockies stations on MWOP in south-central Wyoming, as well as a new interconnect with Kern River Pipeline near the Opal hub. Pipeline meter samples show the expansion began service in mid-Nov ’25.
The MountainWest system provides a critical connection for supply from eastern Rockies basins to demand in the West, including bidirectional flow optionality as market conditions shift. The new expansion on MountainWest Overthrust improves access to the Kern River/Opal corridor in southwestern Wyoming (see map above). Incremental receipts are primarily sourced from Rockies Express Pipeline (REX) at Wamsutter, with a smaller contribution from the Wyoming Interstate Co. (WIC) system near Rock Springs, WY.
Pipeline meter samples show the new westbound capacity on MWOP hasn’t been fully used, likely due to mild temperatures this winter on the West Coast (see figure). However, regional gas prices can blow out during a below-normal season. For example, the 2022-23 winter was particularly harsh across the West in 2022-23, draining Pacific region storage and causing California prices to surge past $40/MMBtu. The next time regional weather and gas prices turn bullish, MWOP shippers can supply more gas to capitalize.
MountainWest Overthrust has other expansions planned, including the Rock Springs Compression expansion to increase capacity on the central Overthrust system by up to 278 MMcf/d. The project would source additional receipts from WIC and MountainWest pipeline, then distribute gas across several meter points for greater regional flexibility. WMB completed an open season on the Rock Springs expansion in October 2024 and is targeting an in-service date of Nov. 1, 2027.
In addition to these compression-driven expansions, MWOP is progressing the Green River West Lateral, a customer-driven project designed to connect the Pioneer processing facility to Opal via the Green River West tap on MWOP. The lateral is expected to provide up to ~64 MMcf/d of transport capacity. WMB is targeting an in-service date of Aug. 1, 2027. By linking the Pioneer plant with MWOP, the project enhances Green River Basin supply optionality at Opal and improves access to western markets.
See East Daley Analytics’ Rockies Supply and Demand report for more information. The targeted expansions by Williams will enhance MWOP’s ability to balance Rockies production, Opal liquidity and downstream western market demand in the years ahead. – Kritika Gaikwad Tickers: WMB.
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