Conventional wisdom – which usually strikes me as something like 95% convention and 5% ‘wisdom’ – holds that returns on technology stocks and energy stocks are largely a function of the business cycle. The theory is that technology stocks generally outperform in the early stages of a bull market, while energy stocks deliver their best returns at about the time that the broad markets peak I should note that while I have chosen to focus on technology and energy for the moment, the full sector rotation/business cycle theory spans all sectors. For those interested in further reading, the CXO Advisory Group has an excellent discussion of a comprehensive business cycle approach to sector rotation (they are skeptical about trading on the theory) and a variety of sources, including Fidelity and Optionetics , have good summary articles. Getting back to energy and technology, I have included below a ratio chart of the AMEX Select SPDRs for the energy ( XLE ) and technology ( XLK ) sectors going back to their 1998 launch. The graph shows an almost perfect negative correlation between the ratio of energy to technology sector performance and the SPX from 1998 through the end of 2003. This time frame is reasonably representative as well, as it includes two bull periods of about 1 ½ years each, as well as a bear market of a little more than two years. From the beginning of 2004 to the present, however, the correlation between the energy to technology ratio and the SPX flips from negative to positive, as energy starts to outperform technology at the same time the markets begin a long bull run. For the past four years, up to and including the current month, energy has generally had the upper hand or at least been the equal of the more ballyhooed technology sector. I find it interesting that the last time the XLE:XLK ratio was this high was July 2006, when the markets were selling off over uncertainty about whether Bernanke would continue to raise the Fed discount rate. Now I won’t go as far as to say that the bull market is officially over if the XLE:XLK ratio gets over 3.0, but keep an eye on this ratio. As US consumers get accustomed to $100/barrel oil and $3.50/gallon gas, any number of things are possible, but I don’t believe the broader markets will continue to rise if energy outperforms technology going forward.