JACKSONVILLE, Fla. - The closer Irma approaches, the farther you might have to travel to find gasoline.

As millions of south Floridians evacuate and head north, the need and lines at gas stations are growing while supplies dwindle. Gate Petroleum is one of many brands that's having to adjust.

"At this point, because demand has been so high at so many of our stores, we are focusing the refueling efforts on stores along evacuation routes and along major interstates," Gate spokeswoman Mindy Skipper told First Coast News on Friday, roughly two days before Irma was expected to begin her hardest impact on the First Coast.

Jacksonville-based Gate Petroleum operates about 100 stores and supplies about another 100 in Florida, Georgia, and the Carolinas. Many gas stations have been running out, at least temporarily, since the start of the week.

"Demand remains high, however we are still delivering product and refueling those stores as quickly as possible," Skipper reminded. "So, there’s a store that may be out temporarily and then, you know, a short period later, be refueled with supply."

The geography of Florida heightens the challenge of an evacuation, said GasBuddy.com senior petroleum analyst Dan McTeague, not only because of a small number of evacuation route options.

"About 97 percent of all the gasoline supplies you have in Florida comes by barge," he said.

One of the major receiving points for southern Florida, Port Everglades near Fort Lauderdale, is already closed. McTeague said others in the Tampa area might follow soon.

"[They] will likely close later in the day," he said. "The matrix that allows for fuel to get in and to be distributed may be interrupted until those ports are reopened, which can only happen when the storm has passed and a damage assessment is made."

Meanwhile, McTeague says drivers can travel smart during the evacuation by using either GasBuddy.com or the smartphone based GasBuddy app, both of which allow access to user-provided data updates including availability and prices. The Web site includes a tracker map that can zoom in on a desired area. The color-coded map gives a quick glimpse of which stations reportedly have fuel (green), those that don't (red), those for which there's no updated status within the last 24 hours (gray), and ones where the power is out altogether (black).

McTeague also has access to percentages of availability in a given region, giving ballpark figures as of mid-day Friday.

"I'd say down there, you're looking at at least 65 percent without now in Miami," he said. "Jacksonville, the other way around, about 65 percent with."

He cautioned that those percentages will likely continue receding unfavorably - especially farther south - in the hours leading to Irma's arrival.

"At some point they will no longer be replenishing, simply because the storm is hitting and we don't want trucks down there either, so those trucks will be more confined to doing runs from terminals as far away as Alabama."

McTeague echoed what many officials have been urging: that travelers limit their fuel purchases to what they realistically need, as courtesy to those who might go without.

"Be mindful that whatever gallons of fuel you take is gallons of fuel someone else may not have, whose situation may be as critical as yours."