A stronger U.S. dollar is compounding an oil market rout that has seen crude prices fall by almost 20 percent this month, and options trades suggest the market is preparing for deeper losses ahead. The accelerated oil price drop since the beginning of the year has been largely blamed on China’s stock market turmoil and its slowing economy, yet the dollar’s strength is emerging as another important bearish factor, traders and analysts said. The U.S. dollar index has risen more than 20 percent since mid-2014 as a relatively robust U.S. economy attracted investor flows from other regions. The Federal Reserve’s first increase in U.S. interest rates in a decade in December and the prospect for further rises are expected to continue underpinning the greenback going forward. Since oil is traded in dollars, a stronger greenback makes it more expensive for countries using other currencies to buy fuel, potentially denting demand.