INSTRUCTOR AND STUDENT RUN OUT OF GAS AND MAKE FORCED LNDG.

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MY STUDENT AND I WERE DOING A XCOUNTRY FLT AND 5 MINS OUT FROM OUR ARPT OF INTENDED LNDG; WE RAN OUT OF GAS. WE WERE IN A C152 WHICH HAS 4 HRS OF USABLE FUEL ON BOARD. WE PLANNED THE FLT TO BE AROUND 3 HRS LONG. AT ABOUT 2 HRS 45 MINS THE ENG STARTED TO SPUTTER AND I THEN DECLARED AN EMER AND LANDED ON A DIRT ROAD. SOME CONTRIBUTING FACTORS TO THIS INCIDENT WERE A 40 KT HEADWIND WHICH THEN DIED; SO OUR TAILWIND ON THE WAY BACK WAS NOT AS STRONG AS WE ESTIMATED IT WOULD BE. ALSO; THE PLANE WAS NOT A GREAT PERFORMER. WE WERE GETTING ABOUT 2350 RPM OUT OF IT. A C152 SHOULD BE ABLE TO GET AROUND 2500 RPM. I FOUND OUT THAT THE AIRPLANE BURNS AROUND 7 GPH WITH THE MIXTURE FULL RICH; AT CRUISE PWR. HUMAN FACTORS: I VISUALLY CHK THE AMOUNT OF FUEL BEFORE WE DEPARTED BOTH AT NORMAN; OK; AND IN SERMAN; TX. THE TANKS APPEARED TO BE FUEL IN NORMAN AND ABOUT 40% FULL IN SERMAN. IT WAS ALSO DARK; SO IT WAS HARD TO TELL. WE FIGURED THAT WE HAD ENOUGH FUEL TO MAKE THE TRIP AND HAVE OUR NIGHT RESERVE ON BOARD; BUT THE CONTRIBUTING FACTOR OF A TAILWIND THAT DIED AND A POOR PERFORMING ACFT; AND WE HAD A CASE OF FUEL STARVATION. THE TOTAL TRIP IS 214 NM. SOME CORRECTIVE ACTIONS THAT I HAVE COME UP WITH ARE TO KNOW EXACTLY HOW MUCH FUEL IS IN THE ACFT; LEANING THE MIXTURE PROPERLY; AND TO PAD MY FUEL CONSUMPTION FOR TAXI; RUNUP AND CLBOUT.