This study examined the effect of firm characteristics on capital structure of listed oil and gas firms in Nigeria for the period 2006-2016. The listed oil and gas firms are ten (10) in numbers out of which a sample of eight (8) was used for the study. Firm characteristics as the independent variable were proxied by; profitability, firm growth, asset tangibility, liquidity and firm size, while the debt to total assets was used as a proxy for capital structure of firms. However, market leverage was used and two leverage ratios (total debt to market value of assets and long term debt to market value of assets) were used to define the capital structure. 

Correlational research design was used in the study. 

The study made use of multiple regression technique and data were collected from secondary source consisting of annual reports and accounts of the firms under study.The findings revealed that all of the explanatory variables (profitability, growth, tangibility, liquidity and size) were significant in explaining the capital structure of the Nigerian listed oil and gas firms. 

However, only profitability was significant to both measures of leverage while the remaining four were significant with only one of capital structure measurements. Profitability and growth both had a significant negative effect on the capital structure of listed oil and gas firms in Nigeria. While on the other hand, tangibility, liquidity and firm size all had positive and significant effect on the capital structure of firms. Based on the findings of the study, it is therefore recommended that management of firms should be profit driven by adopting policies like cost control and cost reduction tools and also by ensuring that their assets are efficiently and effectively utilized in order to generate more sales revenue. This will enable them accumulate substantial retained earnings which may be used to finance future growth opportunities without necessarily opting for excessive debt.