This study aimed to develop a practical method of estimating energy expenditure (EE) during tennis. Twenty-four elite female tennis players first completed a tennisspecific graded test in which five different intensity levels were applied randomly. Each intensity level was intended to simulate a “game” of singles tennis and comprised six 14 s periods of activity alternated with 20 s of active rest. Oxygen consumption (VO 2 ) and heart rate (HR) were measured continuously and each player's rate of perceived exertion (RPE) was recorded at the end of each intensity level. Rate of energy expenditure (EE VO2 ) during the test was calculated using the sum of VO 2 during play and the ‘O 2 debt’ during recovery, divided by the duration of the activity. There were significant individual linear relationships between EE VO2 and RPE, EE VO2 and HR, (r≥0.89 & r≥0.93; p<0.05). On a second occasion, six players completed a 60-min singles tennis match during which VO 2 , HR and RPE were recorded; EE VO2 was compared with EE predicted from the previously derived RPE and HR regression equations. Analysis found that EE VO2 was overestimated by EE RPE (92±76 kJ.h −1 ) and EE HR (435±678 kJ.h-1), but the error of estimation for EE RPE (t=-3.01; p=0.03) was less than 5% whereas for EE HR such error was 20.7%. The results of the study show that RPE can be used to estimate the energetic cost of playing tennis.