Here at SkyTruth we track vessels with satellite imagery, and also with other satellite-collected data. Here's a view of the situation using satellite Automated Information System (AIS) data, radio-frequency tracking information that vessels continually broadcast so they can avoid running into each other at sea:
|AIS map on March 24, 2014 showing ship traffic backed up as a result of an oil spill in the Houston Ship Channel. Colored triangles mark the locations of vessels of different types. Port of Houston is at upper left.|
|Detail from above, showing large offshore holding area where dozens of cargo ships and tankers lie at anchor, awaiting clearance to enter the ship channel (marked by dashed pink line).|
This shows a large "waiting room" in the Gulf just outside the entrance to the channel where dozens of vessels -- mostly oil tankers and cargo ships -- are anchored, waiting for clearance to proceed into port. There are also quite a few vessels bottled up in port, waiting to get out, including a few large cruise ships.
You can see some of the AIS data yourself, and query individual vessels, at the cool Marine Traffic ship-tracking site.