SAN FRANCISCO (MarketWatch) — You’d never know oil’s price is tanking by looking at supplies.

Oil inventories appear to be defying conventional wisdom, hovering near 80-year highs even as prices have tumbled by more than half since crude oil’s peak last June.

A report from trade group the American Petroleum Institute late Wednesday showed a jump of 14.3 million barrels in crude supplies for the week ended Feb. 13 — prompting some following the oil market to call it “ridiculous,” “shocking,” or “gargantuan.”

The action has left oil traders, already whipsawed by swings in oil prices, more confused than ever.

When the U.S. Energy Information Administration released its data early Thursday, the market seemed to breathe a collective sigh of relief, even though the 7.7 million-barrel climb reported by the government agency was more than twice that the 3.1 million-barrel increase analysts polled by Platts expected. Oil futures CLH25, significantly pared their losses on the New York Mercantile Exchange after the EIA news Thursday.

Early Friday, crude-oil futures were trading flat trading at $51.83 in choppy trading.

So why are the inventories soaring?

Supplies are rising due to 9.28 million barrels a day of domestic crude output — the highest since April 1973, and the U.S. also has the most land-based storage for crude because of a “boom by Master Limited Partnerships in the last four years,” which added quite a bit of crude-oil “tankage,” said Tom Kloza, global head of energy analysis for the Oil Price Information Service.

“We’re testing virgin territory for crude-oil stocks,” he said.

“No one really knows what the ‘all full’ level” for storage is, though some reasonable guesses are 450 million to 460 million barrels, Kloza said.

Added to that is what Reuters refers to as the largest U.S. refinery workers strike since 1980, which has come just as refineries are starting their seasonal maintenance, which generally runs from February through late spring.

Slowdowns in refining lessen demand for crude — and so does the strike at West Coast ports.

The “West Coast port mess equals not enough truck movements and not enough diesel demand, so crude oil just backs up all over again,” said Richard Hastings, a macro strategist at Global Hunter Securities.

It’s no wonder that the continuing declines in the number of rigs drilling for oil hasn’t helped alleviate the nation’s supply glut.

Read: These places have lost the most rigs since crude’s collapse

Indeed, U.S. stockpiles of crude continue to grow and the EIA referred to the 425.6 million-barrel total as “the highest level for this time of year in at least the last 80 years.”

It is worth noting that API and EIA reports calculate inventories differently.

“Bottom line is the API data [are] voluntary,” notes John Macaluso, research analyst at Tyche Capital Advisors. But for companies which carry or store 1,000 barrels or more of crude oil, the EIA’s survey is mandatory.

And “it always seems that API tries to catch up with EIA data, which is a much more detailed report,” said Macaluso. Last week, the API said crude stockpiles rose 1.6 million barrels for the week ended Feb. 6, while the EIA said they were up 4.9 million.

But no matter how you measure it, oil’s supply glut doesn’t look like it is set to abate soon.