Energy-use statistics in Tanzania reflect the country's low level of industrialization and development. In 2016, only 16.9% of rural and 65.3% of urban inhabitants in mainland Tanzania were connected to some form of electricity. We use a nationally representative three-wave panel dataset (2008-2013) to contribute to the literature on household energy use decisions in Tanzania in the context of the stacking and energy ladder hypotheses. We firstly adopt a panel multinomial-logit approach to model the determinants of household cooking-and lighting-fuel choices. Secondly, we focus explicitly on energy stacking behaviour, proposing various ways of measuring what is inferred when stacking behaviour is thought of in the context of the energy transition and presenting household level correlates of energy stacking behaviour. Thirdly, since fuel uses have gender-differentiated impacts, we investigate women's bargaining power in the decision-making process of household fuel choices. We find that whilst higher household incomes are strongly associated with a transition towards the adoption of more modern fuels, especially lighting fuels, this transition takes place in a context of significant fuel stacking. In Tanzania, government policy has been aimed mostly at connecting households to the electric grid. However, the public health, environmental and social benefits of access to modern energy sources are likely to be diminished in a context of significant fuel stacking. Lastly, we present evidence that the educational attainment of women in the household is an important aspect of household fuel choices.