PLT OF AN SMA TWIN ENTERED CLASS A AIRSPACE AND OPERATED ABOVE 14000 FT WITHOUT SUPPLEMENTAL OXYGEN.

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SEP/SUN/95 I DECIDED TO TAKE OUR FLT SCHOOL'S SEMINOLE (PA44-180) ON A FLT TO DETERMINE ITS PERFORMANCE AT ALT; IN PREPARATION FOR A POSSIBLE FLT TO COLORADO. DEPARTING AUSTIN'S AIRSPACE TO THE SE; I SQUAWKED VFR AND CONTINUED CLBING. IN AN AREA WHICH I DEEMED TO BE FREE OF AIRWAYS AND TFC; I COMMENCED A CIRCLING CLB. SOON I HAD REACHED 10000 FT AND SOON THEREAFTER; I REACHED 15000 FT. I WAS PLEASED AND SURPRISED THAT THE ACFT PERFORMED AS WELL AS IT DID; SO I CONTINUED. AT A CERTAIN POINT; THE EFFECTS OF THE ALT DEMANDED MORE ATTN BE GIVEN TO THE FUEL MIXTURES AND PWR/PROP SETTINGS. WHILE I WAS TWEAKING THE MIXTURES; I INADVERTENTLY STRAYED INTO CLASS A AIRSPACE. I LOOKED AT MY ALTIMETER AND REALIZED MY ERROR AT 18300 FT (JUST UNDER). I IMMEDIATELY BEGAN A SPEEDY DSCNT; AND FINALLY LEVELED OFF AT 7000 FT. I THEN REALIZED I ALSO HAD FLOWN FOR APPROX 10 MINS ABOVE 14000 FT WITHOUT OXYGEN APPARATUS. CONTRIBUTING TO THIS EVENT: I WAS DISTRACTED BY THINGS INSIDE THE COCKPIT TO THE EXCLUSION OF THINGS OUTSIDE. ALSO; MY RELATIVE INEXPERIENCE WITH HIGHER ALT FLYING SHOWED UP IN MY NOT RECOGNIZING AIRSPACE BOUNDARIES AHEAD OF TIME. ALSO; I SHOULD HAVE STUDIED THE REGS REGARDING SUPPLEMENTAL OXYGEN AHEAD OF TIME.