The mystery has come to haunt Mexico as unrelentingly as one of its beloved soap operas: where is Bermeja, an island off the Yucatan coast that appears to have vanished without trace?

The disappearance of Bermeja is no laughing matter – it would allow Mexico to extend its maritime border some 55 miles further north, helping it to fight off what it sees as American encroachment on its claims to potentially vast oil reserves in the Mexican Gulf.

Hunger for news of the missing island has intensified – along with bizarre speculation about what could have happened to it – as Mexico and America ponder a new drilling agreement.

Mexico’s hunt for Bermeja has been given urgency by BP’s announcement last week of a big find in the Gulf, the latest in a series of discoveries that has turned the area into one of the oil world’s most promising exploration regions.

Some have scented skulduggery on an epic scale and conspiratorially minded Mexican nationalists have seized on the mystery as an opportunity to bludgeon America, a standard reflex when things go wrong south of the Rio Grande.

They accuse the great behemoth in the north of destroying the island – described in some accounts as a sand bar or coral clump and in others as a volcanic rock rising out of the sea – to undermine Mexico’s oil claims. Others argue that natural causes, from rising sea levels to earthquakes, may have brought about the demise of Bermeja, which means bright red in Spanish.

It appears on maps as early as the 1500s and as late as 1941. Mexican Islands, a book published in 1946 by the country’s Institute of Geography, lists Bermeja’s coordinates; so do publications by the distinguished Mexican Society of Geography and Statistics. The longitude and latitude of Bermeja are given on Google Earth and in a CIA atlas. However, Mexican expeditions sent to the island in the past decade have been forced to return home without a glimpse of it.

Doubts about Bermeja’s existence surfaced more than a decade ago but were kept quiet so as not to cause panic. The Alacranes islets much further south were the point of reference for a 1997 treaty on maritime limits between Mexico and America and a 2001 “doughnut hole” accord – a reference to one of the gaps between American and Mexican territorial waters.

Mexican legislators fighting a rearguard action in favour of the island’s existence have been dealt a blow after a land and air search of the region: a report to the Mexican Congress by the National Autonomous University of Mexico concluded that “the island does not exist”.

Elias Cardenas, chairman of the parliament’s maritime committee, said there were four more possible sites where the island might lie. He called for more studies before Mexico and America formalise the next drilling agreement. “Right now, the big fight is for oil,” he said. He did not believe the United States had bombed the island, as some have suggested.

Others took a different view. “There is no doubt the gringos are behind this,” wrote Marco on a nationalist website. “Let’s not forget that they stole California.”

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