The world’s richest oil billionaires had $4.6 billion wiped from their fortunes last week when oil capped the biggest weekly loss in almost 10 months as hopes faded that OPEC will be able to implement a promised deal to cut production and ease global oversupplies. The Organization of Petroleum Exporting Countries met in Vienna last week to attempt to curb output but the meeting ended without a deal being reached. That hit the fortunes of oil producers Harold Hamm, Kelcy Warren and Jeffery Hilldebrand, according to the Bloomberg Billionaires Index.