We apply the Constitution compilation of 397 supernova Ia , the baryon acoustic oscillation measurements including the A parameter , the distance ratio and the radial data , the five-year Wilkinson microwave anisotropy probe and the Hubble parameter data to study the geometry of the universe and the property of dark energy by using the popular Chevallier-Polarski-Linder and Jassal-Bagla-Padmanabhan parameterizations . We compare the simple \chi ^ { 2 } method of joined contour estimation and the Monte Carlo Markov chain method , and find that it is necessary to make the marginalized analysis on the error estimation . The probabilities of \Omega _ { k } and w _ { a } in the Chevallier-Polarski-Linder model are skew distributions , and the marginalized 1 \sigma errors are \Omega _ { m } = 0.279 ^ { +0.015 } _ { -0.008 } , \Omega _ { k } = 0.005 ^ { +0.006 } _ { -0.011 } , w _ { 0 } = -1.05 ^ { +0.23 } _ { -0.06 } , and w _ { a } = 0.5 ^ { +0.3 } _ { -1.5 } . For the Jassal-Bagla-Padmanabhan model , the marginalized 1 \sigma errors are \Omega _ { m } = 0.281 ^ { +0.015 } _ { -0.01 } , \Omega _ { k } = 0.000 ^ { +0.007 } _ { -0.006 } , w _ { 0 } = -0.96 ^ { +0.25 } _ { -0.18 } , and w _ { a } = -0.6 ^ { +1.9 } _ { -1.6 } . The equation of state parameter w ( z ) of dark energy is negative in the redshift range 0 \leq z \leq 2 at more than 3 \sigma level . The flat \Lambda CDM model is consistent with the current observational data at the 1 \sigma level .