U.S. upstream transactions to date have nearly doubled in 2016 following a seven-year low in 2015, triggered by a surge of Permian Basin activity, oil and gas researcher 1Derrick said Tuesday.

Merger and acquisition (M&A) activity to date has reached $58.3 billion, versus $31 billion for full-year 2015. Oil prices began to recover in May to above $45/bbl, leading to a wave of onshore consolidation. International upstream M&A totaled $62.6 billion, a “robust improvement” over $34.2 billion in 2015, excluding Royal Dutch Shell plc’s takeover of BG plc for $82 billion. Russia accounted for $27 billion (43%) of the value.

“U.S. unconventional basins, which are short-cycle plays, benefited from higher oil prices and improved economics from significant cost cutting and operational efficiencies,” 1Derrick Managing Partner Yashodeep Deodhar said. “Both rig counts and M&A activity rebounded as producers in premium plays, such as the Permian, received strong support from equity markets and private investors.”

Domestic M&A dealmaking has accelerated with stabilizing oil prices, climbing rapidly from a slow $5 billion in the first quarter to $58 billion to date in 2016. Mega-deals, valued at more than $1 billion, climbed to 14 from only four last year as producers and private equity investors competed to build-out larger positions in premium plays.

Private equity firms were active on both sides of the table, with 31 acquisitions and 21 divestitures, 1Derrick noted.

Transactions in the Permian year-to-date have accounted for almost $26 billion in value, with more than $20 billion alone since the end of June. The Permian also represented 10 of the 20 largest deals.

“Overall, U.S. unconventional plays represented 18 of the 20 largest transactions,” according to researchers. The number of transactions above $100 million also rebounded to 95 from 59 in 2015, reflecting the health of the M&A markets.

Corporate consolidation this year had been predicted because of the commodity price downturn, but to date there’s only been one big one in the U.S. exploration and production sector — Range Resources Corp.’s $4.4 billion purchase of Memorial Resource Development Corp.

“Buyers overwhelmingly sought to increase positions in premium resource plays, while sellers sought to monetize previous investments as implied values surged after a long lull in M&A activity,” researchers said.

Boosting positions in specific U.S. onshore areas represented eight of the 10 largest transactions — and all have a Texas connection — including:

Canada M&A activity this year has accounted for $15.6 billion of M&A, topped by Suncor Energy’s C$4.54 billion acquisition of rival Canadian Oil Sands Ltd. In otherwise bleak international dealmaking, Russian activity stood out, with three of the largest corporate transactions this year.

“Deal flow in North Sea, Africa, South America and Asia was virtually nonexistent,” said 1Derrick Managing Director Mangesh Hirve. “Outside of Russia and Canada, only five deals over $1 billion were struck.”

Oilfield service transaction value has doubled this year to a six-year high of $52.6 billion, compared with $26 billion in 2015, on two major transactions. The $32 million merger by General Electric’s GE Oil and Gas with Baker Hughes Inc. leads the way, followed by the $14 billion merger of Houston’s FMC Technologies Inc. and Paris-based Technip.

Midstream transaction value for 2016 now totals $145.7 billion, up from $112 billion in 2015, the second highest in the last six years.

M&A activity, which had been slow since early 2015, surged in the second half of the year on two major transactions, the $20 billion merger between Sunoco Logistics Partners LP and Energy Transfer Partners LP, and Canada’s Enbridge’s deal to take over Spectra Energy.

Downstream deal value this year totals $64 billion from $51 billion in 2015 — with nearly all of the activity overseas.