Splitting this off from the
"Longest unsigned interval between gas stations" thread, which also discussed some very long signed intervals between gas stations (like 163 miles between Tonopah NV and Ely NV on US 6) ...
Traveling in eastern Canada earlier this month, I came across signs for some really long gas-free highways, including parts of the Trans-Labrador Highway, the James Bay Road, and the Trans-Taiga Road spur from the James Bay Highway.
Starting off with the Trans-Labrador Highway photos (already posted in another thread):

The one above was taken on the Trans-Labrador Highway just north of Port Hope Simpson. 410 km is about 255 miles, so this tops the
"next services 244 miles" sign at Coldfoot on Alaska's Dalton Highway (AK 11).

This one is from the north end of NL 510 (newer central/southern section of the TLH), south of its junction with the original TLH (NL 500) west of Happy Valley-Goose Bay. 392 km is about 244 miles.
The number on the second sign is smaller than on the first one, because the second one is 18 km west of the gas stations in Happy Valley-Goose Bay. But it actually should be more alarming. Heading north from Port Hope Simpson, gas is available off NL 510 in Charlottetown via NL 514 (about 50 km/31 mi. from PHS, including a 25 km one-way detour from NL 510), and in Cartwright via NL 516 (about 200 km/124 mi. from PHS, including an ~85 km one-way detour). Heading southbound from NL 500, the only way to get gas in less than 365 km/227 mi. (via the detour to Cartwright) is to turn back.
Either way, would this be the longest gas-free interval on a numbered highway anywhere in North America?
I'll post here separately my pix from the unnumbered James Bay Highway, which I traveled a few days after I finished the Trans-Labrador Highway.
Corrected URL link in the first sentence. - Alex