2006 997.1 S, normally change oil (Mobil 1 0w-40 at 4.5 to 5k miles and sooner during hot season. Lately after cars is warmed up and come to a stop (idle) my pressure needle will rest at the .5 bar line, before this summer it would hang a tad above the 1 bar line.
New oil pressure sender installed 2 weeks ago, 1 month prier to that all 4 O2 sensors replaced, plugs, and installed a cooler thermostat (160), temps measured with my OBDII sit around 180 to 187.
Also when cold, well cool here in Valencia California my oil pressure is at 4.5 bar and will hit 5 bar when accelerating, when on highway the oil pressure will reflect RPM.

My next thought would be possibly a warn primary oil pump...

 

Maybe not a worn out pump but with with more clearance that "normal".

Best thing I can recommend is you arrange to take an oil pressure reading at hot idle with a known good pressure gauge.

You must know the true oil pressure before you go on. The oil pressure sensor is not a precision instrument.

If the oil pressure is really 0.5 bar that's still around 7psi. The oil pressure is measured at a point that is quite a distance away from the oil pump.

At hot idle the engine doesn't need a lot of oil pressure so unless the low oil pressure light is on/flashes or you hear lifter ticking that goes away as soon as RPMs and oil pressure rise I do not think there is a problem.

The fact the oil pressure at higher RPMs is apparently within (spec) is also comforting. This indicates the pump can make higher pressure ok.

'course you can (and I recommend it) consult with a professional tech, who will probably take a high confidence oil pressure reading.

True low oil pressure can be from a number of things. The oil pressure valve the controls piston oil jet delivery can be stuck. At some point if the pressure drops enough this should close. If it doesn't the oil pressure will be low.

Another possible explanation is an internal oil leak. There are a number of places where the all that keeps the high pressure oil in the high pressure oil galley is a tight fit between to machines surfaces with a special sealant that fills in the voids of the surfaces. If this sealant "fails" high pressure oil can bleed out and lower oil pressure.

This is most noticeable at low RPMs when the oil pressure is low already and the leak then represents a rather large fraction of the total amount of oil being supplied.

But at higher RPMs the amount that can leak drops to insignificance.

'course, you'll probably never discover the internal oil leak -- if there is one -- unless the engine is torn down and a careful check is made of all the mating surfaces for any sign the sealant has been flushed out by the oil.