Fog halted ship piloting to and from the key oil ports of Houston and Texas City, building a queue of 74 vessels inbound and outbound, the U.S. Coast Guard said.

Pilots on Monday afternoon stopped boarding vessels for transit into and out of Houston, Galveston and Texas City, a Coast Guard spokesman said.

44 vessels were waiting to enter Houston and 16 were waiting to leave. Eleven were waiting to enter Galveston or Texas City and three were waiting to leave, the spokesman said.

Most of the ship traffic into the area is crude oil, petrochemical and petroleum product tankers calling on Houston and Texas City. Galveston has cruise ship, container and offshore oilfield service traffic.

Houston also is a major container and grain port.

The fog was expected to lift by midday but then return late in the afternoon, the Coast Guard spokesman said.

Fog drifts in every winter along the Texas Gulf of Mexico coast. It results from high humidity air encountering colder seawater, which condenses fog out of the air.

Usually, the Coast Guard keeps the ports officially open, but private pilots associations control when ships move by deciding when it is safe to board vessels for transit of the busy, winding Houston Ship Channel.

The 53-mile (85-km) waterway serves all three ports and is lined with one of the world’s biggest concentrations of oil refineries and petrochemical plants. (Reuters)