Past project data sources provide key information for construction cost estimators. Previous research studies show that relying only on one's own experience during estimation results in estimators' bias. Having and referring to historical databases, containing objective information on what happened in past projects, are essential for reducing estimators' biases. The first step toward development of useful project history databases is to understand what information estimators require from past projects. The research described in this paper targets estimators' information needs identified through interviews, brainstorming sessions, task analyses, and card games conducted with estimators with different experience levels and specialized in heavy/civil and commercial construction projects, and exploration of historical and standard databases available in companies to determine what is being currently represented. Findings show that estimators need contextual information, depicting the conditions under which specific production rates were achieved, so that they can identify which production rate would be more realistic to use during the production rate estimation of an activity in a new bid. Comparison of the contextual information needs identified in this research with information items available in historical data sources (such as company cost reports, RSMeans, previous studies) highlighted some gaps and important opportunities for improvements in those sources. The identified contextual information items are significant for practitioners in developing ways to augment their existing project history databases to make them more beneficial for estimators.