This is a Tale of Two Hybrid Systems.

In 2007, General Motors introduced a gas-electric hybrid powertrain, with the catchy name of Belt Alternator Starter, or BAS, in the Saturn Vue SUV and Aura sedan, as well as the Chevrolet Malibu sedan.

General Motors then joined forces with Mercedes and Chrysler to co-develop a much more sophisticated system that it called the “2-Mode Hybrid” drivetrain, which was introduced in 2008 in the Chevrolet Tahoe and GMC Yukon full-size SUVs, and used very briefly in the 2009 Saturn Vue, before Saturn was killed off in GM’s 2009 restructuring.

The main difference between the two, without getting into the serious nitty-gritty, is that the 2-Mode system can drive the vehicle on electricity alone at low speeds, while the BAS setup works in tandem with the gas engine to boost power in acceleration. The common thread is that both are designed to shut the gas engine down when the car is stopped in traffic.

The old BAS system left me unimpressed every time I tested it. It never lived up to its claims of reduced fuel consumption in real-world driving, so I wasn’t sad when it disappeared with the Saturn brand in 2009.

Imagine my excitement, then, when Buick, another GM division, announced it would use a second-generation BAS hybrid drivetrain in a pair of its cars: the full-size LaCrosse, and the car you see here, the mid-sized Regal. It’ll be available in the 2013 Chevrolet Malibu, too, which comes out early spring of 2012. Hybrid version of all three cars use the eAssist model designation.

GM claims some improvements this time around — namely a larger battery and a more powerful electric motor, both of which are said to increase the amount of electric assist. The Regal eAssist’s fuel consumption estimates, according to Natural Resources Canada, are 8.3 L/100 km in city driving and 5.4 L/100 km on the highway. At first glance, that’s not a lot better than the last Saturn Aura to use the first-generation BAS, which was rated 7.9 in the city and 5.8 on the highway.

Like I said, BAS never impressed me in its previous applications, and I’m not thrilled about this new system, either: the Regal eAssist averaged 9.5 L/100 km in a mix of city and highway driving and 7.2 L/100 km on an all-highway, Ottawa-Toronto round trip. That’s the best fuel efficiency I’ve seen in any Regal I’ve tested — this is the third version of this car I’ve driven — but that’s faint praise, as the gas-only models weren’t particularly thrifty. A four-cylinder Toyota Camry managed similar fuel economy without the aid of hybrid power, and I’ve seen similar economy in cars like the Hyundai Sonata, Kia Optima and Lexus ES 350.

Let me say that I like the Regal. It’s a nicely-sorted car that handles well and is quite nice to drive, and whose only drawback in a general sense is that its interior is a little snug compared to other mid-size sedans.

With all that said, General Motors has two questions to answer: Why does it need a hybrid drivetrain in order to build a four-cylinder, mid-sized sedan as fuel-efficient as its competition? And, if it’s going to bother with a hybrid, why not use the far-and-away better 2-Mode system in these sedans and make a real go of it? The 2-Mode drivetrain must have cost a fortune in R&D, money that I can’t imagine is being made back that quickly in the few big hybrid SUVs and pickups GM sells. My best guess is that GM’s post-restructuring alternative-propulsion budget went into developing the Chevrolet Volt, a great car that was certainly worth what it cost to design and whose general excellence certainly raised my expectations for what future GM hybrids would (and should) be.

Like other hybrid sedans, the Regal eAssist’s battery eats into trunk space, and it costs more, to the tune of about $3,000, when you account for the extra features it includes that are options on the basic four-cylinder Regal. It’s been suggested that Buick will ditch that regular base model in favour of the eAssist, a tactic that will only work if they bring the price down.

Options on the Regal eAssist I drove included a $1,885 package that added heated leather front seats and a power-adjustable front passenger seat, while navigation and a power sunroof cost $995 and $1,395, respectively. The bottom line was further padded with $650 for bi-xenon headlights and rear-seat side airbags for $450, and remote engine start (an ironic addition to a car marketed as a fuel-saver) added $275. All of this drove the MSRP from its $34,335 starting point to $39,905 before freight and taxes.

My problem with the Regal eAssist is not that I don’t like the car. It’s that General Motors has done so much to fix the problems that nearly drove it out of business a few years ago. The problem, now, is that I expect more from GM than a re-hashed and half-assed hybrid drivetrain.