The terrorism threat level in the United States has been elevated to “orange” for the nation’s mass transit systems.

That’s one level below the highest threat category of “red.”

The increased alert level comes in the wake of apparent terrorist bombings on London subways and buses Wednesday morning.

At least 20 people were killed and many more injured.

British Prime Minister Tony Blair is calling the bombings “acts of terrorism.”

The tragic events are further proof of how sensitive the global oil market is. Right after the bombings – in subway tunnels, on subway trains and on buses – crude oil prices dropped by $4 a barrel.