Even after all the ground lost by oil prices in the second half of the year, 2014 will be remembered as the year of the megadeal—deals of at least $1 billion that stormed the acquisition and divestiture (A&D) box office.

Megadeals lead the record breaking year with 49 transactions worth $266.1 billion in value compared to 24 deals worth $71 billion in 2013, according to PwC US.

For all deals, 2014 racked up 252 worth $321.5 billion, an increase from the 187 deals worth $117.2 billion in 2013, PwC said. However, the firm said that low oil prices may drive a surge in restructurings in 2015.

The fourth quarter of 2014, and particularly December, saw the E&P market start to stall as oil prices dipped. However, megadeals still represented 91% of total deal value in the quarter.

In last three months of 2014, 57 oil and gas deals valued at more than $50 million accounted for $128.7 billion, an amount that dwarfed by 200% the $43 billion on 56 deals in the fourth quarter of 2013.

“While 2014 was a very strong year for oil and gas deal activity, we saw a steady decline in November and December as the drop in oil prices accelerated, contributing to a marked shift in deal sentiment from playing offense to playing defense as companies focused on maintaining liquidity,” said Doug Meier, PwC’s U.S. energy sector deals leader. “That downward trajectory in oil prices, coupled with the impact of leverage, drove a number of deals related to corporate restructurings and portfolio right sizing activities.”

In the current low-price environment, the effects of debt could drive additional deal activity as leveraged companies look to strengthen their balance sheets by focusing on cash flow optimization and operational efficiencies, he said.

Fourth-Quarter Break Down

Deals in the final stretch of the year were remarkably robust despite the rapid drop in crude oil prices. From June to December, West Texas Intermediate (WTI) fell about 44%.

Megadeals took charge. For all of 2014, there were 49 megadeals worth $266.1 billion, accounting for 83% of total deal value.

Even in the troubled fourth quarter, megadeals accounted for 15 transactions worth $117.5 billion. That was a 345% increase over the $26.4 billion on eight megadeals seen in the fourth quarter of 2013.

For relatively smaller deals, with values of at least $50 million, 16 corporate transactions totaled $103.7 billion in the fourth quarter of 2014. For the year, all corporate transactions contributed $227.5 billion on 59 deals.

Asset transactions still dominated total M&A deal volume during the fourth quarter of 2014.

Asset transactions hit $25 billion, accounting for 19% of total deal value for the fourth quarter of 2014. For all of 2014, 193 asset deals added $94 billion in value.

Overseas Investors

After being largely absence in North America, foreign investors continued to show interest in the U.S. as both deal value and volume were at 10-year highs, contributing 56 deals worth $71.2 billion in 2014.

In the fourth quarter, foreign buyers announced 15 deals, making up $25.4 billion, a 25% increase in deal volume and a 426% increase in value compared to the fourth quarter of 2013.

For midstream companies, 2014 was the year midstream began to sew up large parts of basins with breathtaking deals.

“The midstream was a fairly sleepy part of the industry historically and has grown very quickly in the past few years to kind of meet this need,” John England, Deloitte’s vice chairman, U.S. Oil & Gas, told Hart Energy.

PwC counted 19 midstream deals contributing $53 billion in value, a 111% growth in deal volume and a 276% increase in deal value compared to the fourth quarter of 2013.

Upstream deals accounted for 25 transactions worth $32.5 billion. That figure doesn’t take into account the $76 billion Kinder Morgan Inc. (NYSE: KMI) spent assembling its partners back into one giant company.

Shale, Other Sectors

Seven oilfield services deals matched the 2013 total, but total deal value increased $36 billion, a 619% jump. The total was a 10-year high compared to $5 billion in the fourth quarter of 2013. The standout oilfield services deal was the acquisition of Baker Hughes Inc. (NYSE: BHI) by Halliburton (NYSE: HAL) for $34.6 billion. The deal is expected to close in the second half of 2015.

Shale deals continued their dominance among deals. According to PwC, there were 24 transactions worth at least $50 million related to shale plays in the fourth quarter of 2014, totaling $57 billion—a 139% increase from the fourth quarter of 2013.

For the year, 107 total shale deals contributed $110.3 billion, a 107% growth of money changing hands compared to 2013.

Among upstream deal makers, shale saw 19 transactions worth $14.9 billion, or 76% of total upstream deals in the fourth quarter of 2014. Five midstream shale-related deals in the fourth quarter of 2014 accounted for $42.1 billion, a 230% increase from the fourth quarter of 2013.

“Overall 2014 shale deal value and volume surpassed 2013 highlighting the continued interest from investors in U.S. shale plays, especially in the upstream space, which contributed 79% of total shale deal activity,” said John Brady, a Houston-based partner with PwC’s energy practice. “However, a sustained low oil price environment is driving an intense focus on returns and the deployment of assets to the most efficient shale plays.”

The most active shale plays during the fourth quarter of 2014 include the Bakken ($3.1 billion) and Permian ($2.4 billion). The Marcellus Shale’s three deals were worth $5.7 billion. The Eagle Ford also contributed three deals worth $484 million.

During 2014, MLPs were involved in 48 transactions, representing about 19% of total 2014 deal activity, consistent with recent historical levels, PwC said.

Although financial investor deal activity dropped, they continued to show interest in the oil and gas industry with four total transactions, accounting for $2 billion during the fourth quarter of 2014, compared to nine deals worth $10 billion during the same period in 2013.

“In the second half of 2014, we saw financial investors remain active in assessing deal activity across the value chain,” said Rob McCeney, PwC U.S. energy & infrastructure deals partner. “If the price of oil continues to drop or remains at its current levels for a sustained period, we may see financial investors look to actively manage portfolio investments and search for new opportunities with distressed assets.”

PwC’s Oil & Gas M&A analysis is a quarterly report of announced U.S. transactions with value greater than $50 million analyzed by PwC using transaction data from IHS Herold.