As I pulled in to the service station for the first fill-up in this test, with 504 miles showing on the tripmeter, I was thinking warm thoughts about the X-Type diesel estate. Its un-Jaguarlike fuel economy had a lot to do with this, of course, but there was more to it than that.For a start, I like the way it looks, both inside and out. I'm happier with the X-Type saloon's shape than other people seem to be, but I'd be the first to claim that the estate is several degrees more handsome yet. And the fact that Jaguar is clearly happier to be building large, luxury saloons than medium-sized estates - which counts against the X-Type in many ways - at least means that owners of the company's smallest model benefit from Jaguar's superb ability at creating interior ambience. Even after many hours behind the wheel, it's always a pleasure to glance around the passenger area.The two-litre turbo diesel engine is essentially the same TDCi unit fitted to various Fords, and although I'm not convinced by claims that it has been made super-quiet for the X-Type (it seems only averagely refined for the class) it's unquestionably a fine unit. Although it's the least powerful engine fitted to any Jaguar, and produces only moderately interesting performance figures, the real-world effect is more impressive.Once you're up and running, a small squeeze on the accelerator pedal results in a useful surge which comes in handy whether you're looking to make a quick lane change on a motorway or wanting to squirt across the apex of a corner on a twisty back road.In two-litre form, the diesel engine is available only with front-wheel drive transmission - Jaguar reckoned it didn't have enough spare power for the alternative 4x4 system on the X-Type. As I've said in the past, I don't believe that Jaguar really knows what to do with front-wheel drive, but I also reckon it makes a better job of it on the diesel X-Types than on the petrol ones.In this case, handling is by no means class-leading, and both the cornering ability and the ride quality are compromised by a rocking motion which briefly occurs every time the X-Type encounters a bump in the road. There doesn't appear to be anything Jaguar can do about this, since we've experienced it with the saloons and also with cars which have (like this one) or do not have sports suspension.Since I was all on my lonesome during my long journey in the car, I didn't need much luggage space. The X-Type estate has a lot of this, though. With the rear seats up, there's 445 litres to the bottom of the window and 685 litres if you fill the car to roof level. Fold down the seats and you have access to a very competitive 1415 litres. The space can be reached by opening either the whole tailgate or just the rear window.A certain amount of uncertainty surrounds the X-Type. In twenty years' time the "small Jaguar" may prove to have been nothing more than an experimental oddity. For the moment, though, it's an appealing medium-sized car, though hardly one that will be persuading rival manufacturers that they have to rethink their concepts. And in estate form especially, it's an uncommonly pleasing car to have sitting outside your house. Engine 1998cc, 4 cylinders Power 128bhp Fuel/CO2 50.3mpg / 149g/km Acceleration 0-62mph: 9.9 seconds Top speed 125mph Price £23,165 Details correct at publication date