Reuters: US President Barack Obama said today that offshore oil drilling could only go forward if there were assurances that a disaster like the massive Gulf of Mexico oil spill would not happen again. As Obama officially unveiled a commission to investigate the accident, he issued a stern message that while keeping pressure on firms involved in the still-uncapped spill – BP, Halliburton and Transocean Ltd – he would also hold Washington accountable for mending its ways. With …