Processes for the combustion and gasification of coal present challenging instrumenta-tion problems. The combination of high temperatures (2,000°-3,000°F), high pressure (100-1,000 psig), corrosive atmospheres, and erosive conditions create difficult sensor design and material problems. As advanced processes (e.g., entrained gasifiers) are pursued, sensors must fulfill additional performance requirements such as higher accuracy and faster response time in order to meet process safety and control needs. This paper is divided into two major sections. The first section provides background information on fossil energy processes. The second section describes a technique developed to enhance combustion spectroscopy by reducing the interference caused by blackbody radiation. This technique, named BLOC (Blackbody Observation and Cancellation), can reduce the effects of blackbody radiation by 20 dB or more. The two sections presented are: Section I -- Fossil energy background. Section II -- Combustion emission line spectroscopy.