As I understand it you are not allowed to make a profit from the flight.
I'm not aware of any restriction that prevents you from accepting the
free use of an aircraft - and if it was an issue re sharing you could
have made the instructor PIC on the return leg.
That's how it would work in Canada.
In the US? I'll leave someone else to address that one.

Tony
--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE


In article ,
"Joe Johnson" wrote:

Last week, as I returned to my rental FBO after an evening local flight, the
clerk on duty said an instructor and his student were stuck at an airport
about 40 minutes away. I spoke to the instructor on the phone and I agreed
to fly up and bring them back. He mentioned that, of course, I wouldn't
have to pay for the aircraft time. Did I violate the terms of my PPL by
accepting free time in the airplane as "compensation" for picking them up
and bringing them back? Should I therefore have paid a proportional share
of the costs?