"The oil hit sandy beaches mostly," Linden said, "and was therefore easier to clean up, though some of the cleanup in those days was not very carefully done."
Some oil on beaches was bulldozed under, but long stretches of beach were left alone where the oil weathered to tar and then to asphalt, said Jernelöv.
"Five years later, most of this was covered with sand," he added. "But where it was exposed, crabs were crawling over it and oysters and mussels were settled on it. The toxicity of it was gone. It looked like asphalt road."
The spill killed thousands of birds, Jernelöv said. "Maybe up to 10,000, which is a large number if you see them in one spot, but spread over a large distance. It was not like Exxon Valdez."
Researchers estimated 250,000 seabirds were killed by the Valdez spill.
By August 1979, oil reached the Texas shoreline, said Erich Gundlach, an independent consultant with E-tech International, Inc, who assessed shorelines and clean-up for Ixtoc I. "I never believed it would reach that far, but it did."