AbstractThis paper is one of a series published during 2000 to coincide with the launch of an advanced drilling system known as "Anaconda". This drilling system utilises a manufactured carbon fibre composite tube in place of conventional steel drill pipe or coiled tubing. The composite tube incorporates wires built into the wall, making it possible to transmit all the available formation evaluation and drilling data to surface continuously and in real-time.This paper focuses on the impact of this real-time data availability on the ability to make real-time geosteering decisions. In particular we focus on:The uncertainty associated with wellbore planning at seismic resolution when compared with the fine resolution required for modelling log responses and planning well bore trajectories. The issues associated with planning well bores in geological space instead of geometrically are also explored. The issues relating to wellbore planning before the well is drilled and in particular the forward modelling of the anticipated log responses. The practical implications of having all the normal formation evaluation data available in real-time whilst drilling a well. These include handling large data volumes and the ability to reach well decisions in significantly shorter time frames. The software systems developed to deliver the ability to update the geophysical and geological interpretation in the time frame required to influence a well path. The technology which makes it possible to steer the drill string effectively in real-time as new data becomes available. The organisational implications for such real-time decision making – such as high-speed reinterpretations under operational time pressures. The business benefits that might derive from this real-time decision making capability – such as reduced numbers of geological sidetracks, ability to terminate a wellbore at the most appropriate time and maximising the productivity of the wellbore.