A Sussex Police spokesperson said a lorry driver parked in a lay by on the A24 at Southwater on Sunday (November 9).
He awoke at 6.30am the next day to discover that the fuel tank was empty and 200 litres of diesel had been stolen from the vehicle.
On Wednesday (November 12), another lorry driver awoke at 4am in his vehicle on the A264 at Faygate to find half of his diesel tank had been siphoned and the fuel stolen.
Police have asked lorry drivers to stay vigilant and secure fuel tanks if possible.
Police are appealing for witnesses. Anyone with information can contact police on 101 or email [email protected] quoting serial 0223 of 10/11.