Shell Lubricants technical experts suggested that the company implement a field trial to compare the fuel economy benefits of Shell Rimula R4 L 15W-40 to Shell Rimula R5 LE 10W-30. Six Volvo trucks running more or less the same duties were selected for the trial, which took place over a period of six months. Three trucks started with Shell Rimula R4 L 15W-40, the other three with Shell Rimula R5 LE 10W-30. After 3 months, this was switched to prevent any possible truck-specific deficiencies. Throughout the trial, fuel consumption was closely monitored by Volvo Fleet management on-board computers.