Shell has launched a double Avios promotion across its full range of fuels. It will run until July 31st.
During this period, you will earn 20 Avios for every 20 litres of Shell fuel you buy.
You need to be a member of Shell Drivers Club in order to collect Avios. You swipe your Shell card each time you buy petrol, and set up your Shell account to automatically convert your points to British Airways Executive Club every quarter.
This is my lengthy post from earlier in the year on the best way to earn Avios when buying fuel. Even with double Avios, you will earn more miles by using Tesco instead – but if you are nearer to a Shell, this offer is a decent bonus.
Please note, though, that taking Avios from Shell Drivers Club is not necessarily the best use of your points. 4,000 points, for example, gets you 2,000 Avios or a £20 Shell or Waitrose voucher. Unless you value Avios at more than 1p, you are better off taking a voucher, which is effectively as good as cash.