Oil giant Shell misled consumers by claiming its fuel was able to take drivers further, the Commerce Commission says.
Shell is defending 22 charges under the Fair Trading Act in Wellington District Court.
The charges relate to brochures and print, television, radio and billboard advertising from April 2006 to May 2007, in which Shell claimed a fuel economy formula added to its petrol was "designed to take you further".
Commerce Commission lawyer John Dixon told the court today that the advertising made false or misleading claims, and the company had engaged in conduct that was liable to mislead the public.
The ads gave consumers the impression that fuel containing Shell's additive could take them appreciably further.
However, a peer-reviewed study commissioned by Shell found the additive had an average benefit of only 0.98 percent over petrol with no additives.
A driver who spent $2000 on fuel petrol year would save only about $20 from using the additive, Mr Dixon said.
The hearing is set down for four days.
NZPA