(John Kemp is a Reuters market analyst. The views expressed are his own)
* Chart 1: tmsnrt.rs/1NV47Y4
* Chart 2: tmsnrt.rs/1NV4dyW
* Chart 3: tmsnrt.rs/1NV4emv
* Chart 4: tmsnrt.rs/1NV4jXg
By John Kemp
LONDON, Dec 17 (Reuters) - U.S. crude oil imports have accelerated over the last four weeks, pushing commercial crude inventories within a whisker of the record set in April.
Crude imports surged to 8.3 million barrels per day (bpd) last week, up from 7.0 million bpd four weeks earlier, according to the U.S. Energy Information Administration (tmsnrt.rs/1NV47Y4).
Imports are running at the fastest rate since September 2013, with almost all the extra crude arriving at ports along the U.S. Gulf Coast. (tmsnrt.rs/1NV4dyW)
Both the timing and the location are unusual because refineries and traders try to minimise stocks held along the Gulf Coast at year-end to avoid storage taxes imposed by Texas and Louisiana.
Faster imports have pushed crude stocks higher even as refiners have boosted the amount of crude they process to a seasonal record 16.6 million bpd.
Crude imports are notoriously volatile: while pipeline imports from Canada are somewhat regular and stable, tanker imports from other countries are much more variable.
Each very large crude carrier (VLCC) arrives with around 2 million barrels of crude, which is recorded in U.S. inventories once it has cleared customs.
The timing of ship arrivals and customs clearances can therefore have a big influence on reported weekly import volumes.
Heavy seaborne imports one week are often followed by a sharp drop the following one due to the timing of ship arrivals.
But the past four weeks have seen a fairly unusual and sustained increase in imports along the Gulf Coast, where imports have risen from the equivalent of around 9 VLCCs to 14 VLCCs per week.
Most of the additional crude has come from Saudi Arabia (roughly an extra two tankers per week), Mexico (one to two tankers per week), Venezuela (one tanker) and Iraq (one tanker). The reason for the upsurge in seaborne imports is not clear (tmsnrt.rs/1NV4emv).
The reason could be purely timing-related as tankers unload now after being delayed in transit or unloading back in November.
Or crude could be flowing to storage facilities in the United States because it is easier and cheaper to store there as terminals in the Caribbean, Europe and Asia fill up.
There are also strong commercial reasons to put oil into storage in the United States. The contango is running at nearly $1 per barrel per month on average for the first six months (more than enough to cost of financing the inventory and leasing tank space).
Traders have a strong incentive to source as many surplus cargoes as possible from oil exporters in the Middle East and Latin America and bring them to the United States (tmsnrt.rs/1NV4jXg).
The sudden increase in importing could be a sign the market is running out of storage in other locations, in which case the rise in imports and inventories can be expected to continue through the end of the year and into the first quarter of 2016.
On the other hand it may be a short-term storage-related trading play, in which case import levels could revert to a lower level in the next few weeks. (Editing by Dale Hudson)