Of course, my title asks the wrong question. The more policy relevant question is "How much does the NZ Emissions Trading Scheme affect retail petrol prices?
The Ministry of Business Innovation & Employment has a page on weekly oil price monitoring and some week by week data on petrol prices.
I made a R chart from that data.
The NZETS component of the NZ retail price of petrol pretty much just hugs the zero point on the vertical axis.
A note lower down the web page states "The costs associated with the ETS are provided by Hale & Twomey based on the prevailing carbon price from the New Zealand Carbon Market". So we need to note that this data is an estimate.
Over the four and a half years of the NZETS, the estimated NZETS component has ranged from a maximum of 2.4 cents per litre from late 2010 to June 2011 to a minimum of half a cent from July 2013 to December 2014.
As far back as 2007, the Labour Government predicted that petrol prices may rise up to 4 cents a litre possibly based on carbon price of $25 per tonne. From memory, the early 2011 price for a NZ unit was about $21 a tonne.
Wikimedia Commons has the R script I wrote for the chart (except it's a .svg file, not a .png).