U.S. Democratic presidential hopeful Barack Obama has chosen Delaware Senator Joseph Biden to be his vice presidential running mate. Obama's campaign team had tried to keep the decision secret, but about three hours before it began sending official confirmation messages to supporters and journalists, several US networks leaked the news. With a track record of more than 35 years, Biden's selection is expected to counter critics who accuse Obama of lacking international experience. The likely Republican Presidential candidate - Senator John McCain - is still to announce HIS choice for the No. 2 spot.