Domestic merger and acquisition activity across the energy sector last year may have been off from 2012, but offerings for master limited partnerships (MLP) were a standout, as operators looked for investments to buildout onshore infrastructure, according to PwC.

PwC in a webcast on Thursday brought together a group of partners to share insights into last year’s dealmaking. As others already have reported, fewer deals with less total values were a hallmark of transaction activity in 2013, as operators focused on cutting chunks of their noncore assets to maximize efficiencies.

However, that wasn’t true of the MLP sector, where initial public offerings (IPO) continue to increase, said partner Joseph Dunleavy, who specializes in transaction services.

Across all markets, U.S. IPO activity was “tremendous,” he said, raising just under $57 billion, levels not seen since 2007, when close to 300 IPOs raised about $65 billion.

“In the energy space, we have seen an increase in the number of energy IPOs and a more substantial increase in the proceeds,” Dunleavy said. “Activity is up in the energy space, but what’s more interesting is the increase in the number of MLP IPOs, jumping from 14 in 2012 to 20, with proceeds of up to $5 billion.”

That enthusiasm is seen continuing this year.

“Given the pipeline that we can see, the level of requests and activity that we’re seeing, we’re confident that the outlook is pretty optimistic. Absent, of course, a substantial market correction, whatever that might be defined as, we are confident that we’ll continue to see robust activity.”

The confidence is in the numbers, Dunleavy said. Today there are 115-120 energy-related MLPs in the United States.

“What’s really interesting about those numbers would be that roughly half of those MLPs in the energy space have come into existence in just the last four years…While you may look at the energy sector as not being so active in the IPO space, if you look at the MLP sector, it is booming. The activity is tremendous, the focus on it is tremendous…”

In 2013, 24 energy-related IPOs raised about $10.9 billion. Of that, 20 were MLPs with proceeds of $5.2 billion.

That compares with 2012, when 21 energy IPOs raised $5.8 billion, including 14 MLPs that garnered $3.5 billion. The numbers show steadily increasing enthusiasm for U.S. MLPs. There were only two from 1980-1990, with 42 between 2000 and 2009. However, between 2010 and 2013, the U.S. energy-related MLP market had grown to about 111. Since the end of last year, there have been a few more announced, Dunleavy said.

It takes roughly 90-120 days to create a MLP, with registration statements filed with the U.S. Securities and Exchange Commission. Over the last four years, MLPs have averaged 110 days to go public; last year it took about 90 days.

What makes MLPs so attractive is their business structure, taxed as a partnership and publicly traded, which offers liquidity.

“If you look at the U.S. MLP infrastructure, the need for growth within the midstream business and the need to build out our capacity from a transportation perspective, upgrade or update our capacity, the MLP is perfect for achieving that goal,” said Dunleavy.

PwC’s Douglas Meier, a partner in transaction services, said the U.S. energy sector overall in 2013 was more focused on value creation to maximize shareholder value, reducing the value and the deals made. Selling noncore assets was a priority, as was creating more efficiencies in development.

There also were some issues in late 2012 that may have dampened interest in dealmaking through the first half of 2013, Meier said. PwC estimates total deal values declined from 2012 by 24% to $115.9 billion. The number of transactions last year also fell to 182 from 212.

However, a lot of 2012 activity occurred in 4Q2012, in part on uncertainty for 2012 in the capital markets, he said. Many were concerned about U.S. tax law changes last year, which resulted in an “acceleration in deal activity” late in 2012. That in turn slowed activity in the first six months of 2013. By 3Q2013, the number of transactions had risen to 43, only two fewer than in the same period of 2012.

“So there’s a theme that while transaction volumes did decline over 2012, the drop in value was significantly higher, meaning there were fewer large transactions last year…2013 was the year of spinning of businesses to create value,” said Meier. “As companies continue to maximize shareholder value, there will be a continued interest in M&A activity in the sector throughout 2014.”

The current factors that are going to influence the “sustainability” of the U.S. exploration and production sector’s offerings boils down to several factors, according to PwC.

Commodity price outlook is the top influence, followed by unconventional development costs and infrastructure buildout. Whether liquefied natural gas exports influence domestic markets could play a significant role in more MLP offerings. In addition, the “technology evolution” will play a role, as will evolving environmental regulations and shareholder activism.