A C152 PVT PLT VOICES CONCERNS OVER POSSIBLY FLYING CLOSER TO CLOUDS; WITH RESPECT TO VERT SEPARATION; THAN PLANNED WHEN W OF EUG; OR.

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BEFORE DEPARTING CORVALLIS (CVO) ON A FLT DIRECT TO AURORA ARPT (UAO); I RECEIVED A WX BRIEFING FROM FLT SVC. THE BRIEFING INDICATED VFR CONDITIONS AND CEILINGS AT EUGENE (EUG); WHICH WAS DIRECTLY ALONG MY FLT PATH AND ALT OF 6500 FT. I DEPARTED CORVALLIS AND IT BECAME EVIDENT THAT THE CEILING WAS LOWER THAN RPTED; SO I CHOSE TO CRUISING ALT OF 2300 FT MSL. THE CLOUD BASES APPEARED TO BE BTWN 2900-3000 FT MSL; THIS ALLOWING FOR MANDATORY CLOUD CLRNC MINIMUMS FOR CLASS D/E AIRSPACES. I RECEIVED CLRNC TO; AND TRANSITIONED VFR; EUG'S AIRSPACE AT 2300 FT; JUST TO THE E OF THE ARPT. THE CTLR AT EUG TWR TWICE INQUIRED ABOUT THE HT OF THE CLOUD BASES. TO HIS FIRST INQUIRY I GAVE HIM THE MSL ALT OF 2900 FT AS MY ESTIMATE FOR CLOUD BASES. ON THE SECOND INQUIRY THE CTLR INQUIRED ABOUT THE BASE OF CLOUDS THAT WERE TO MY L APPROX 3000-4000 FT. I RESPONDED THAT THE CLOUDS TO MY L WERE APPROX 2700 FT MSL (THIS STILL PROVIDING CLOUD CLRNC MINIMUMS). AFTER LEAVING EUG'S AIRSPACE; I LISTENED TO ATIS TO MAKE SURE I HAD THE CURRENT ALTIMETER SETTING. AT THIS TIME I HEARD THE RPTED CEILING TO BE LOWER THAN I HAD ESTIMATED. I THEN REALIZED THAT I MAY HAVE BEEN CLOSER TO THE CLOUDS THAN I ESTIMATED. THE RPT WAS FROM A POS W OF MY RTE OF FLT AND NOT FOR MY EXACT POS. NEVERTHELESS; IT IS POSSIBLE THAT I WAS CLOSER TO THE CLOUDS THAN I ESTIMATED; AND THAT I BROKE VFR CLASS D CLOUD CLRNC MINIMUMS. THIS POSSIBLE ERROR ON MY PART WAS IN NO WAY INTENTIONAL; AND COULD HAVE BEEN AVOIDED EASILY. IN RETROSPECT; I SHOULD HAVE LISTENED TO EUG ATIS DIRECTLY BEFORE ENTERING THEIR AIRSPACE TO FIND OUT RPTED CLOUD BASE HT; INSTEAD OF RELYING ON MY ESTIMATION. IN THE FUTURE; I WILL UTILIZE FORECASTS MORE INTELLIGENTLY IN DECISION MAKING. I WILL ALSO GIVE MYSELF A LARGER MARGIN OF ERROR -- ESPECIALLY WHEN ESTIMATION IS A DECIDING FACTOR. THIS IS AN ERROR I HOPE TO NEVER MAKE AGAIN; AND ONE THAT HAS TAUGHT ME A VALUABLE LESSON TOWARDS SAFER FLYING.