Executive Vice President & Chief Operating Officer at ONEOK
Thank you, Walt. In our natural gas liquids segment, total NGL raw feed throughput volumes increased 5% compared with the second quarter of 2021 and 10% year-over-year, averaging nearly 1.3 million barrels per day, our highest NGL volume to date. Third quarter raw feed throughput from the Rocky Mountain region increased 5% with the second -- compared with the second quarter 2021 and nearly 50% compared with the third quarter 2020. Volume growth was driven by increased producer activity in the region, ethane recovery and increasing volumes from recently connected third-party plants, including a 250 million cubic feet per day third-party plant that came online in July.
Raw feed throughput volumes from the Mid-Continent and the Permian Basin also increased. Permian volumes increased 12% compared with the second quarter 2021, driven by higher ethane recovery and producer activity levels. We also connected an additional third-party plant in the basin during the quarter. The segment was also able to utilize our integrated assets to capture the benefit of location and commodity price differentials during the third quarter, providing additional earnings on top of our primarily fee-based results. Petrochemical demand continues to strengthen as facilities have returned to normal operations following Hurricane Ida and as the pandemic recovery continues. two new petrochemical plants coming online before the end of the year could provide more than 160,000 barrels per day of additional ethane demand once fully operational.
This additional capacity, combined with strong ethane exports, should support a wider ethane to natural gas differential in 2022. Ethane volumes on our system in the Rocky Mountain region increased compared with the second quarter 2021 as we incented additional ethane recovery during the third quarter. Recovery continued in October and is also expected throughout November, given current regional natural gas and ethane prices. In other regions, we continue to forecast partial ethane recovery in the Mid-Continent and near full recovery in the Permian for the remainder of the year. All of these assumptions are included in our increased financial guidance for 2021. Any additional ethane recovered would provide upside to our 2021 expectations.
Discretionary ethane on our system is now more than 225,000 barrels per day. Of that total opportunity, more than 125,000 barrels per day are available in the Rocky Mountain region and 100,000 barrels per day in the Mid-Continent. As NGL volumes continue to grow across our systems, so does the discretionary ethane. Moving on to the natural gas gathering and processing segment. In the Rocky Mountain region, third quarter processed volumes averaged nearly 1.3 billion cubic feet per day, a 2% increase compared with the second quarter 2021 and nearly 25% increase year-over-year. Scheduled plant maintenance at four of our processing facilities, which have since come back online, decreased third quarter volumes by approximately 30 million cubic feet per day for the quarter.
We estimate that approximately 14 to 15 rigs, which can drill approximately 300 wells per year, is enough to maintain 1.4 billion cubic feet per day of production behind our system. Any additional rigs, combined with the rising gas to oil ratios of wells already connected to our system would provide additional volume growth. Conversations with our producers in the region continue to point to higher activity levels through the end of the year and into 2022. There are currently 32 rigs and 10 completion crews operating in the basin, with 17 rigs and five completion crews on our dedicated acreage. This is more than enough activity to grow gas production on our acreage. In addition to the rigs currently operating in the basin, there remains a large inventory of drilled but uncompleted wells with more than 520 basin-wide and approximately 300 on our dedicated acreage, compared with about 400 DUCs on our dedicated acreage at this time last year.
In the third quarter, we connected 72 wells in the Rocky Mountain region. And in October, we connected more than 30 additional wells. Based on the most recent producer completion schedules, we still expect to connect more than 300 wells this year. With our Bear Creek plant expansion and related compressor stations now complete and in service, we should see a significant number of well completions in the fourth quarter in Dunn County as producers have timed their completions with the start-up of our expansion to avoid flaring. The new plant will accommodate increasing volumes as it ramps to full capacity over the next two to three years. With Bear Creek II's completion, we now have approximately 1.7 billion cubic feet per day of processing capacity in the basin.
We continue to see increased activity in the Mid-Continent region, with two rigs now operating on our acreage and 10 wells connected during the third quarter. Sustained higher natural gas and NGL prices to drive a continued increase in activity next year. During the third quarter, the gathering and processing segment's fee rate averaged $1.02 per MMBtu compared with $0.94 per MMBtu in the third quarter of 2020. Changes in our average fee rates continue to be driven by our volume and contract mix each quarter. We still expect the fee rate for 2021 to average between $1 and $1.05 per MMBtu. On to the natural gas pipelines segment. This segment's stable fee-based earnings continued to drive solid results, with adjusted EBITDA increasing 8% compared with the prior quarter.
As we enter the winter heating season, we continue to see increased interest from customers for additional long-term transportation and storage capacity on our system following the extreme winter weather events earlier this year. The segment's market connected pipelines and more than 52 billion cubic feet of natural gas storage provide critical services to customers year-round, but especially during the winter. As always, we're working with our customers to understand their needs and to help meet increasing demand in the coming months. Pierce, that concludes my remarks.