This cost-benefit analysis of three industrial bottom gillnet fisheries that operated in SE/S Brazil during 2009, had a double purpose: to determine the economic and financial performance of the average gillnet vessel in the coastal whitemouth croaker (Micropogonias furnieri), the gulf hake (Urophycis mystacea) and monkfish (Lophius gastrophysus) fisheries and to determine the expected effects of applying fishing gear regulation (MPA/MMA Nº12/2012) on the performance of the whitemouth croaker fishing fleet. Crucial to this cost-benefit analysis was to collect data through interviews to vessel owners on these fishing fleets cost structures and their fishing costs levels. Three economic and financial performance indicators were used to assess the condition of these fishing fleets: Net Present Value (NPV), Internal Rate of Return (IRR) and Profitability Index (PI). Results showed different costs levels between fishing fleets but, similar relative importance of cost components across fleets: with running costs being the highest, followed by vessel and labor costs in order of importance, except in the gulf hake fishing fleet. Results from the economic and financial performance assessment showed that these three fishing fleets were in a fragile economic and financial condition, all having IRRs lower that 20% and PIs of 1.7 or lower, too low for a high risk activity like fisheries. This problem been more acute in the whitemouth croaker fishing fleet with the lowest IRR (12.11%) and PI (1.2). Potential effects of applying the fishing regulation showed marginal improvements in the fragile condition of the whitemouth croaker fishing fleet.