The 2014 BMW i3 electric car is now in U.S. dealership,  and early examples are eagerly being taken home by drivers--but, so far, only the battery-electric version is on sale.

Despite hundreds of cars parked at multiple U.S. ports, the so-called i3 REx model, which includes an optional two-cylinder engine to act as an emergency range extender, has not yet gone on sale.

DON'T MISS: 2014 BMW i3 Electric Car: Why California Set Range Requirements, Engine Limits

That's apparently because of a delay in printing the so-called "Monroney" document--known as the window sticker--that provides details of the manufacturer's suggest retail price (MSRP), countries of origin for major components, and EPA battery range and fuel-efficiency ratings.

2014 BMW i3 electric cars waiting at East Coast shipping port for distribution, May 2014

2014 BMW i3 electric cars waiting at East Coast shipping port for distribution, May 2014

The delay is detailed on a blog maintained by BMW electric-car enthusiast Tom Moloughney, and its cause appears slightly mysterious.

[UPDATE: BMW's Dave Buchko released the following statement around 11:30 am this morning:

We are moving as quickly as possible to release the first BMW i3 Range-Extender models to BMW i Centers. Receipt of test data from the EPA is one step, but not the final step, in the process of receiving certification from the EPA.

Rules do not permit the release of vehicles for sale until EPA labels are finalized, produced and affixed to any vehicle. Barring any unforeseen delays, we expect that to happen by the end of this week.]

BMW i3 REx models have been arriving in the U.S. for several weeks now, but they're being held until the window sticker can be finalized, printed up, and applied. No vehicles can be sold without one.

MORE: 2014 BMW i3 Range-Extended Model Gets Full $2,500 CA Rebate For Electric Cars

First delivery of 2014 BMW i3 electric car, to Tufts professor Charles Rabie in Boston, May 2014

First delivery of 2014 BMW i3 electric car, to Tufts professor Charles Rabie in Boston, May 2014

The EPA told the office of Washington state representative Chad Magendaz [R-5th District] that it had provided BMW with the results of its BMW i3 REx testing on May 13.

"EPA tested the i3 REx and provided the results of that testing to BMW on May 13th," wrote Linc Wehrly, Director of the EPA's Light-Duty Vehicle Center Compliance Division.

"EPA is not aware of anything that would prevent BMW from importing the vehicles since May 13th."

Representative Magendaz posted the response yesterday afternoon in a Facebook group for BMW i3 enthusiasts.

Thus the ball appears to be in BMW's court.

2014 BMW i3 (German-market version), Amsterdam, Oct 2013

2014 BMW i3 (German-market version), Amsterdam, Oct 2013

While advocates speculate that perhaps one of three ratings had come in lower than BMW expected, leading the company to explore last-minute software updates to improve the ratings, the explanation remains unclear.

ALSO SEE: First Review In: 2014 BMW i3 Range Extender Performance Limited

The EPA ratings include electric range (in miles), electric-mode efficiency (in MPGe), and fuel economy in range-extending mode (in MPG).

The range-extended version of the BMW i3 is expected to have a lower electric range and lower efficiency than the battery version, because its engine, gasoline tank, and associated plumbing make it several hundred pounds heavier.

In the absence of official comment from BMW, the wait continues.

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