The island of 400 residents consumes about 360,000 litres of diesel a year to run its electricity generators while it waits for an eco-friendly alternative to be established.
Southland District Council island representative Cr Jon Spraggon said if there were "major increases" the remote community could take a major hit.
"At the moment everyone’s going on about it, but as far as the island’s concerned, the only one that’ll really be the big effect is the diesel for the generators.
"But it’ll be the cost of getting stuff to the island as well."
The Stewart Island Electricity Supply Authority received weekly updates from its bulk fuel supplier, but the most recent update had not arrived yet, he said.
Residents were being charged about 84c a unit for their power, but he did not want to speculate on how prices would change, he said.
Locals were advised to look at how to save on using electricity and how to save on using fuel.
Cr Spraggon said he expected the electricity supply authority would need to tap into its financial reserves which could provide a buffer against price fluctuations.
"The reserves are fairly substantial at the moment.
A council spokeswoman said the impact of fuel prices would be monitored and once the council understood the possible duration and quantity of any price increase, there would be "discussion with the Stewart Island-Rakiura Community Board about the impact and possible options".
"While [the electricity supply authority] does have reserves, this is not specifically held as a buffer for fuel prices. It is primarily for the replacement of assets but is at times used to fund operational expenditure when the community board considers it appropriate."
However, Cr Spraggon said rising fuel prices were not just hitting residents via the power meter.
Ferry and airline connections were also expected to increase in price, he said.
He said he expected residents making the inter-island commute would consolidate their trips.
And Rakiura’s fishing industry would also be significantly impacted.
Islanders were concerned but ever-practical about the situation.
Stewart Island fishing charter operator Gordon Leask said islanders were worried about rising diesel and electricity prices. There were ways around it, though.
While petrol on the island had risen from $3.60 to more than $4 a litre, the small roading network limited travel.
"We only have 32km of road, so we don’t do a lot of miles. We might have to walk home from the pub once a week or something to save some fuel."
Mana Charters skipper Shane Bryan said keeping a bulk fuel supply had provided a limited financial buffer for his fishing charter business, but acknowledged the situation was critical.
He currently paid $2.80 a litre for diesel, but at $3 a litre he would stop making a profit.
"If it doesn’t change in the next month, we’ll be struggling to survive ... we’ll just be out the back door."
While he was personally less concerned about fluctuating electricity prices, as his home operated on multiple fuel supplies, locals were generally uneasy, he said.
"I can see the uneasiness in everybody... but Stewart Island’s a pretty relaxed place."
If the island’s fuel supply ran dry, it would also affect the wastewater system.
"If they can’t get fuel to the island ... there’s going to be no power ... you can’t flush your toilets then, can you?
"They’ll probably want us evacuated off the island ... that could be a big picture as well."
Real Journeys had also reduced its seasonal daily strait crossings from three to two crossings earlier than usual as the domestic market had dwindled.
Real Journey’s Foveaux ferry skipper and former SS Earnslaw skipper Ryan Little said he was feeling the cost of commuting from Cromwell to Invercargill every four days in his "back pocket".
While the cost of the commute had almost doubled it, it was still cheaper than commuting daily to Queenstown and dealing with Queenstown’s traffic congestion, he said.
