Every day, around 80 oil and gas tankers typically pass through the Strait of Hormuz, the narrow waterway off Iran's southern coast that carries a fifth of the world's oil and a significant amount of natural gas. On Monday, just two oil and gas tankers appear to have crossed the strait, according to a New York Times analysis of shipping activity from Kpler, an industry data firm. Since then, one tanker passed through. "It's a de facto closure," said Dan Pickering, chief investment officer of Pickering Energy Partners, a Houston financial services firm.