This paper introduces a novel algorithm for jointly estimating carrier frequency offset and I/Q imbalance for OFDM systems. The new algorithm is a closed form solution to obtain the frequency offset and I/Q imbalance parameters in the absence of noise. In the presence of noise, the proposed algorithm uses the least squares algorithm to accurately estimate the parameters. The proposed algorithm is thus very scalable in terms of complexity. While the target system is OFDM, the proposed algorithm applies to any system as long as two identical data blocks are received in the receiver. Simulation results show that given a suitable amount of CFO, the high estimation accuracy of the proposed algorithm makes its BER performance comparable to a system without CFO and I/Q imbalance.