There seem to be two 'correct' options for the 2.0 diesel Mondeo.
Firstly the handbook states that the engine oil should be to Ford specification WSS-M2C913, now to revision C, with a recommendation to use Castrol or Ford oil.
It also says "if you are unable to find an oil that meets the specification defined by WSS-M2C913-C, you must use SAE 5W-30 that meets the specification defined by ACEA A5/B5."
Secondly, there's a lot of information about oil suitable for engines equipped with DPFs. There are relatively new ACEA specifications, C1, C2, C3 and C4, which are "designed for use in high performance gasoline and light duty diesel engines where advanced aftertreatment systems such as Diesel Particulate Filters (DPFs) and Three Way Catalysts (TWC) are used." Ranging from C4 down to C1, the SAPS (Sulphated Ash, Phosphorous and Sulphur) limits are always mid to low while the HTHS (High-temperature, High-shear) vary from high for C4 down to low for C1. The C1 and C2 levels also have increased fuel economy requirements.
This recommendation has also come from the fact that the engine used in the Mondeo is also common across the PSA Group range (Citroen, Peugeot) who have been recommending ACEA C2/C3 oils since the introduction of their PSA B71 2290 standard in 2009.
The common reasoning given for the fact that Ford still recommend ACEA A5/B5 in their manual and dealer network is that the ACEA C ratings were not fully established at the time of the Mondeo's release, however that clearly hasn’t stopped Citroen and Peugeot from adapting.
It looks like Ford has tried to alleviate some of the issues presented to motorists on engine oil selection by releasing a new standard: WSS-M2C934, now to revision B. This is classed as "an extended drain engine oil for vehicles equipped with diesel particulate filter (DPF)." From what I’ve seen on places like Opieoils and oilspecifications.org this is a Ford specification that is also to ACEA C1. The range of Jaguar Land Rover engines such as the 2.7d and 3.0d are using this WSS-M2C934-B standard as well.
In the end, I purchased 6 litres of Motul Eco-clean+ 5w-30 ACEA C1 which is to the specifications of WSS-M2C934-B, ACEA C1, Mazda engines with DPF and JASO DL-1. Others on here are recommending saving a little money and going for an ACEA C2 oil which admittedly will have marginally better wear properties but marginally increased fuel consumption. As long as you use an oil rated to ACEA C2 or C1 I like to think that the DPF on the Mondeo's will last the car's lifetime.
I hope this helps someone else with their decision on which engine oil to buy!
Edited by mlwprescott, 26 February 2013 - 10:59 AM.