Despite some planned mega-mergers, market uncertainty meant few companies were willing to join forces in last year's weakened energy economy, analysis finds.

An emailed report from consultant firm IHS found the value of merger and acquisitions in the oil and gas sector declined 22 percent last year to $143 billion. That's despite the planned $85 billion merger outlined in 2015 by Royal Dutch Shell and BG Group.

"Unstable oil prices caused outlook uncertainty in 2015, and this lack of stability, a key ingredient for buyers and sellers to reach consensus, caused fewer deals to be reached," Christopher Sheehan, director of merger and acquisition research at IHS, said in a statement.

Crude oil prices started falling below the $100 market in mid-2014. Brent, the global benchmark price for crude oil, closed trading Tuesday at $36.42 per barrel, off about 35 percent from the start of 2015. This market scenario translated to volatility making it difficult for potential buyers and sellers to reach a consensus on the way forward.

IHS found the number of energy sector deals last year was at its lowest level since 2001. Global spending, meanwhile, dipped below $30 billion last year after topping $75 million in 2014.

Sheehan said weakness should endure throughout the year as most analysts expect slow economic recovery will keep markets skewed heavily toward the supply side.

"We believe the likelihood for wider consolidation in the oil and gas industry will increase in 2016 as producers face further financial pain and will have more constrained financing options due to persistently weak oil prices," he said.

Shell and BG shareholders consider the merger at the end of January.