Discoveries of new oil and gas reserves dropped to their lowest level in at least two decades last year, pointing to tighter world supplies as energy demand increases in the future.

Preliminary figures suggest the volume of oil and gas found last year, excluding shale and other reserves onshore in North America, was the lowest since at least 1995, according to previously unpublished data from IHS, the research company.

The slowdown in discoveries has been particularly pronounced for oil, suggesting that production from shales in the US and elsewhere, and from Opec, will play an increasingly important role in meeting growing global demand in the next decade.

New finds of oil and gas are likely to have been about 16bn barrels of oil equivalent in 2014, IHS estimates, making it the fourth consecutive year of falling volumes. That is the longest sustained decline since 1950.

Because new oilfields generally take many years to develop, recent discoveries make no immediate difference to the crude market, but give an indication of supply potential in the 2020s.

Peter Jackson of IHS said: “The number of discoveries and the size of the discoveries has been declining at quite an alarming rate . . . you look at supply in 2020-25, it might make the outlook more challenging.”