A disconnect between buyer and seller expectations after the plunge in crude oil prices depressed M&A activity in the oil and gas sector in 2015, but that gap is likely to close as oil prices remain depressed so dealmaking should pick up this year, according to global consultancy IHS. Global oil and gas transactions slumped 22 per cent in value in 2015 to $US143 billion, despite the boost from Royal Dutch Shell's $US85 billion agreement to buy BG Group, IHS said in its newly released M&A report.