By MarketWatch SAN FRANCISCO (MarketWatch) - Oil and gas stocks tumbled after Tuesday's open amid falling crude-oil prices and concerns that China's economic growth is slowing. The Conference Board's revision for its April leading economic indicator for China was steeply lower, raising concerns over China's ability to prevent a slowdown of the global economy. With that revision came a steep drop in U.S. markets. The Dow Jones Industrial Average (DJIA 9,903, -235.49, -2.32%) fell 282 points to 9,856. The August crude-oil futures contract was last down $2.63 to $75.64 a barrel, a 3.4% drop, as Tropical Storm Alex traveled farther west away from the oil and gas rigs off the Louisiana coast. BP PLC (BP 27.49, +0.44, +1.63%) said Monday that waves created by Tropical Storm Alex will delay implementing the next phase of oil containment by six or seven days, but existing containment efforts won't be affected by the storm. Alex sustained winds of 70 mph Tuesday, the National Hurricane Center reported. A storm needs to maintain winds of 74 mph to become a Category One hurricane. The NYSE Arca Oil Index (XOI 896.10, -19.81, -2.16%) dropped 2.29% to 894.78 points Tuesday morning. Just one of its 13 components was up during morning trading, with BP gaining 1.11% at $27.33. The NYSE Arca Natural Gas Index (XNG 489.91, -14.79, -2.93%) slipped 2.76% to 490.75, and the Philadelphia Oil Service Sector Index (OSX 166.47, -4.77, -2.79%) dropped 3.19% to 165.78 points.

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