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shale and other reserves onshore in North America, was the lowest since at least 1995, according to previously unpublished data from IHS, the research company. Depending on later revisions, 2014 may turn out to have been the worst year for finding oil and gas since 1952.