Complex sentence: A particular challenge may be the fact that refiners are set up to produce a certain fuels mix from crude oil including diesel and petrol, with some grades, such as aviation fuel likely to be required for the foreseeable future.
Split into simpler sentences: A particular challenge may be the fact that refiners are set up to produce a certain fuels mix from crude oil, including diesel and petrol. Some grades, such as aviation fuel, are likely to be required for the foreseeable future.