West Texas Intermediate futures for August delivery dropped sharply to $52.69 (-7.45%); Brent crude climbed to $56.96 ( 0.74%) after yesterday's drop. Both crudes declined to their lowest levels since mid-April. Massive declines in oil prices were caused by the result of Greek referendum, which showed that the majority of Greece's citizens rejected lenders' austerity terms and generated more concerns over the country's membership in the euro zone. This led to declines in the single currency against the dollar. A strong dollar tends to pressure oil as it makes imports more expensive for holders of other currencies. The recent rise in U.S. drilling rigs and a potential increase in supplies from Iran put extra pressure on oil.