Singapore wealth fund Temasak has bought a five percent stake in Spanish oil group Repsol for just over one billion euros, raising its total stake in the company to 6.3 percent, Repsol said Monday. Temasak bought Repsol\'s entire portfolio of treasury stock at 16.01 euros per share for a total of 1.036 billion euros ($1.35 billion), the company said in a statement. \"The operation, the biggest investment ever made by Singapore in Spain, reflects the confidence which first class international investors have in Repsol\'s growth strategy,\" it said in a statement. Repsol unveiled a new strategic plan in May after Argentina nationalised oil and gas producer YPF, in which it had a 51 percent stake, that focuses on boosting oil exploration and reducing its net debt to avoid a possible downgrade by credit rating agencies. As part of the strategy the company said it would invest 19.1 billion euros between 2012 and 2016 to develop new exploration projects, mostly in Algeria, Brazil, Bolivia, Russia, the United States, Spain, Peru and Venezuela. Temasek has been boosting investments in the energy sector, which accounted for 6.0 percent of its portfolio in its last financial year that ended in March, up from 3.0 percent a year earlier.