This paper will discuss the development and applications of Bragg grating-based array temperature sensing (ATS) that is used for SAGD heavy oil applications. A Bragg grating-based pressure and temperature gauge has also been developed and successfully implemented for SAGD monitoring applications. The sensing systems have demonstrated long lifetimes and reliable operation for many years in very hostile, hydrogen-rich environments. These wells typically have temperatures exceeding 250°C and pressures nearing 1,000 psi. The applications are ideally suited for the capabilities of fiber optic sensing and harsh environments.