The optical detection of methane gas usually requires an open cell with light propagating through it as the detection system This implies the need for precise and, therefore, often expensive and delicate alignment optics. The Letter reports, for the first time, the use of a continuous optical fibre link as the absorption system, thereby obviating the need entirely for precision optics. The system uses a suitably designed section of D-fibre as the interaction mechanism. Initial experimental results indicate that resolutions in the region of 100 parts per million of methane should be achievable.