Pilot scale measurements play an important role in our understanding of the coal gasification process. To gain the most practical benefits from such testing it is important to have a good understanding of the fundamental processes that influence coal behaviour under industrial conditions. In this paper, a suite of Australian coals was characterised in detail at the laboratory scale and preliminary assessments made of their likely performance under practical entrained flow conditions. The same coals were then tested using a 5 MWth pilot-scale entrained flow gasifier in Part 2. The resulting gasification dataset for a suite of coals at both laboratory and pilot scale provides a unique opportunity to quantify the links between laboratory gasification measurements and coal gasification behaviour under realistic conditions. This paper presents a characterisation of four Australian thermal coals in terms of their slag formation and flow behaviour, coal devolatilisation and reactivity properties, and their gasification conversion behaviour. This work provides the basis for a relative assessment of their potential for use in entrained flow gasification, and identifies possible performance issues which may need consideration for use in larger-scale gasification systems. The second paper discusses the pilot-scale gasification behaviour of these coals, and relates those data with those presented here. (C) 2011 Elsevier B.V. All rights reserved.