A re-analysis of Gliese 581 HARPS and HIRES precision radial velocity data was carried out with a Bayesian multi-planet Kepler periodogram ( from 1 to 6 planets ) based on a fusion Markov chain Monte Carlo algorithm . In all cases the analysis included an unknown parameterized stellar jitter noise term . For the HARPS data set the most probable number of planetary signals detected is 5 with a Bayesian false alarm probability of 0.01 . These include the 3.1498 \pm 0.0005 , 5.3687 \pm 0.0002 , 12.927 _ { -0.004 } ^ { +0.006 } , and 66.9 \pm 0.2 d periods reported previously plus a 399 _ { -16 } ^ { +14 } d period . The orbital eccentricities are 0.0 _ { -0.0 } ^ { +0.2 } , 0.00 _ { -0.00 } ^ { +0.02 } , 0.10 _ { -0.10 } ^ { +0.06 } , 0.33 _ { -0.10 } ^ { +0.09 } , and 0.02 _ { -0.02 } ^ { +0.30 } , respectively . The semi-major axis and Msini of the 5 planets are ( 0.0285 \pm 0.0006 au , 1.9 \pm 0.3 M _ { \earth } ) , ( 0.0406 \pm 0.0009 au , 15.7 \pm 0.7 M _ { \earth } ) , ( 0.073 \pm 0.002 au , 5.3 \pm 0.4 M _ { \earth } ) , ( 0.218 \pm 0.005 au , 6.7 \pm 0.8 M _ { \earth } ) , and ( 0.7 \pm 0.2 au , 6.6 _ { -2.7 } ^ { +2.0 } M _ { \earth } ) , respectively . The analysis of the HIRES data set yielded a reliable detection of only the strongest 5.37 and 12.9 day periods . The analysis of the combined HIRES/HARPS data again only reliably detected the 5.37 and 12.9d periods . Detection of 4 planetary signals with periods of 3.15 , 5.37 , 12.9 , and 66.9d was only achieved by including an additional unknown but parameterized Gaussian error term added in quadrature to the HIRES quoted errors . The marginal distribution for the sigma of this additional error term has a well defined peak at 1.8 \pm 0.4 m s ^ { -1 } . It is possible that this additional error arises from unidentified systematic effects . We did not find clear evidence for a fifth planetary signal in the combined HIRES/HARPS data set .