OIH had a makeover in late 2011 as the old 'Oil HOLDRS' was taken over by Van Eck and turned into a living, breathing ETF, with new management, and a simple strategy aimed at capturing the 25 largest and most liquid US-listed oil services companies. Although a fraction of its portfolio is focused overseas, OIH overweights the US and makes its own sector bets. Overall, the OIH offers extremely concentrated exposure with a strong bias to US-firms. The index is rebalanced semi-annually.