SrRuO3 (SRO) thin films were grown on SrTiO3 (100) substrates using the pulsed laser deposition method. The films' growth properties widely changed in response to different working oxygen partial pressures. An island growth mode was dominant for low pressures up to 10 mTorr followed by a step flow growth mode at 60 mTorr and step flow plus 2 D growth at 200 mTorr then reverting back to island growth at 300 mTorr. Significant out-of-plane strains of SRO films were observed for low growth pressures (up to 10 mTorr) but became notably reduced at 60 mTorr and continued to decrease gradually with further pressure increases. Formation of Ru vacancies occurs regardless of the working pressure values and appears to be minimized at 60 mTorr. Highest TC's were obtained in films exhibiting the step flow growth mode. The role of Ru deficiencies in relation to strain, growth mode, and magnetic properties is discussed.