Russian state-run oil giant Rosneft has pledged to invest around $100 million in geological prospecting and drilling off Vietnam after it received approval for a new oil bloc there, RIA Novosti reported on Wednesday citing Rosneft CEO Igor Sechin. The Rosneft head signed a production-sharing agreement for the bloc on Wednesday between TNK Vietnam, a subsidiary of TNK-BP taken over by Rosneft, and Vietnamese state company Petrovietnam. Sechin said geological prospecting for the new block would take about two years but did not specify the amount the company might spend on the whole project.