Website says 6l/100km but I think this was obtained under controlled circumstances ie. top speed of 80kmh, gear change at 2000rpm, no overtaking, new lubes, new tyres, proper tyre pressure. It's possible to achieve if you like an arse. But nobody buys a BMW to be driven like that. It's meant to highlight the frugality although I think it's not realistic here. In short, it's for marketing purpose.
I drive the 320d while website claims 4.5l/100km, the best I ever did on a long trip to Singapore and back to KL and then to Klang and then back to KL plus abit of town driving in between, was about 4.8l/100km. Did it in a full tank that lasted 1,300km. I drove like an arse, ecopro all the way with a top speed of 110kmh and average of maybe 90kmh.