. 2006. Developing statistical models to estimate the carbon density of organic soils. Can. J. Soil Sci. 86: 295-304. Carbon density is a key variable in assessments of local or regional soil carbon (C) stocks, but its direct measurement on large numbers of samples is both time-consuming and expensive. To assess whether the C density of organic soils can be inferred from other parameters, we examined the ability of field-(stratigraphic depth and material type) and lab-(bulk density and ash content) based variables to predict the C density of organic soil samples. Candidate models given three different levels of a priori information about samples were developed from data for continental western Canada and examined using Akaike's information criterion (AIC). Models at each level were then used to predict profile-level C storage in cores from three different regions (continental western Canada, Ontario, and the Northwest Territories). In profiles from western Canada, predictions were unbiased, with mean prediction errors of 0-7% and local precision depending on the amount of a priori information available. Application of models to other regions yielded mixed results, probably reflecting both differences in site characteristics and classification/analytical methods used. Since these error sources are impossible to separate given available data, we recommend that models for C density prediction should be tailored to a given research question and region. The results suggest that simple, field-based variables are sufficient to predict C density for the purpose of regional surveys. To obtain accurate estimates at the profile level, bulk density (and ash or C content) have to be measured in the lab. . Les profils de l'Ouest canadien donnent des prévisions non biaisées avec une erreur moyenne de 0 à 7 %, la précision locale dépendant du volume d'informations a priori disponible. L'application des modèles à d'autres régions donne des résultats mitigés, sans doute à cause des variations au niveau des caractéristiques du site et des méthodes de classification ou d'analyse employées. Ces sources d'erreur ne pouvant être séparées des données existantes, les auteurs préconisent qu'on adapte les modèles de prévision à une région et à un problème scientifique particuliers. Les résultats laissent croire que des variables simples, relevées sur le terrain, suffisent pour prévoir la densité du carbone dans le cadre d'études régionales. La masse volumique apparente (ainsi que la concentration de carbone et la teneur en cendres) devra être mesurée en laboratoire si l'on veut en obtenir une estimation plus précise au niveau du profil. Abbreviations: ASH, ash content (% or proportion of sample weight); AIC, Akaike information criterion; C I , inorganic carbon content (% or proportion of sample weight); C O , organic carbon content (% or proportion of sample weight); C T , total carbon content (% or proportion of sample weight); BD, bulk density (g cm -3 ); COR, carbon/organic matter ratio; CD, carbon density (g cm -3 ); D, depth (cm from...