LONDON, July 27 (Reuters) - Oil climbed on Thursday, with Brent crude topping $84 a barrel for the first time since April, supported by supply tightness owing to OPEC+ production cuts and renewed optimism on the outlook for Chinese demand and global growth. Crude has posted four consecutive weekly gains on an expected tightening of supply because of output cuts by the Organization of the Petroleum Exporting Countries (OPEC) and its allies, known collectively as OPEC+, as well as some involuntary outages. See here for a complete list of exchanges and delays