The spatial distribution of chemical species can be a critical determinant of the performance of chemical reactors. One such reactor is the combustion chamber of the Internal Combustion engine, in which the spatial variation of air-fiiel ratio has a significant influence on both fuel efficiency and emissions performance. We report the development of a fibre-based Near Infra-Red Absorption Tomography system, in order to measure the distribution of hydrocarbons in-cylinder. The technique exploits the specific (but weak) hydrocarbon absorption of 1.7 µm radiation, which wavelength has only recently become accessible for the present application by the availability of solid-state all-optoelectronic components. A custom-specified InGaAsP/InP laser diode has been supplied, delivering 3mW at 1.700µm, with about lnm tunability. A standard telecommunications laser diode is used to provide a reference wavelength at 1.55 µm, which is not absorbed by any species in the combustion environment. Along each of 32 absorption paths through the subject, both wavelengths are launched simultaneously via a single-mode optical fibre and GRIN lens. The transmitted light is collected by a large-core fibre and measured by an extended-sensitivity InGaAs photodiode. The attenuation at each individual wavelength is measured by modulating the intensity of the laser sources in a frequency-division multiplexed scheme. The logarithm of the ratio of the two measurements yields the path integral of the hydrocarbon absorption, and hence, of concentration. Single-channel characterisation shows that the technique is readily calibrated for temperature and pressure effects, over the region 70- 150°C and 1- 10bar. Tomographic reconstruction of different gaseous hydrocarbon flows has been achieved. Design considerations will be discussed concerning the deployment of the technique to a running engine, to achieve image rates over 10,000 per second.