If you look at Citroen's own specs, the 1.9D gives 40.9 mpg, only just over two more than the 1.6 which gives 38.2. The HDi is supposed to do 49.6, but if you read the report on the AA's website (theaa.com), they say they struggled to get anything like that! Their tests came up with just 5mpg more than the HDi, which means you'd have to drive a lot more miles (and be slower getting there!) to make it worthwhile. The Picasso with the same HDi engine is more more economical.