This paper set out to investigate the relationship between investment payback periods of offshore wind farms and operational factors such as reliability and O&M. Additionally, it was suggested that a comparison with capacity factor would help contextualise the importance of operational issues. No reliability threshold was discovered as such, since it was clear that all levels ofreliability evaluated were acceptable from the viewpoint of paying back the investment in 6 years at the most, even with a relatively low capacity factor of 28%. This is probably due to the increased level of revenue generated as a result of reforms to the UK renewable obligations system, which may make offshore wind farms an attractive investment for utilities. Elsewhere, feed-in tariff systems will produce a similar effect of the subsidy is set at an adequate level. It should be noted, however that the assumption of 1 M per MW installed offshore may be conservative and the same may be said of the assumption of 50,000 per turbine per year in the case ofTBM, since these costs are not yet well understood. The most significant result is that the reliability of individual wind turbine components can have an appreciable effect on payback period for the wind farm. While this shows reliability to be less significant than capacity factor, in some cases the influence is as much as 60 % of CF influence. This seems to back up the theory that reliability will be an important issue for future offshore wind farms, and perhaps be considered as significant as estimating the wind regime at a potential site. Finally, in most of the cases a time based maintenance policy was the most cost-effective. Further a crossover point will exist at which condition-based maintenance becomes the most cost effective option. If the system is very reliable, the economic argument for CBM no longer exists. Nevertheless, industry opinion seems to be that meeting high reliability targets will be a challenge for offshore wind turbines owing to environmental conditions, meaning that the crossover point will be reached and thus enabling CBM.