I would now like a turn the call over to your host, Dave Barger. Please go ahead, sir.
Thank you, John, and good morning, everyone, and thank you for joining us today. This morning, we are pleased to report record second quarter net income of $52 million or $0.16 per diluted share, an improvement of $27 million compared to the second quarter of 2011. This marks our ninth consecutive quarter of profitability. We achieved a 10.2% operating margin, a 2.7 point improvement over last year. We're particularly pleased with the margin expansion we are able to achieve as we generated record revenues, evident that our network strategy is working.
JetBlue ended the quarter with approximately $1.2 billion in unrestricted cash and short-term investments or 25% of trailing 12 months revenue. Due to our strong liquidity position, we're able to strengthen our balance sheet during the quarter by reducing debt, including approximately $170 million in debt prepayments. These results would not have been possible without the hard work and dedication of JetBlue's 14,000 crew members who deliver an unrivaled customer experience to our customers each day. As a testament to our high-quality product and the experience that our crew members delivered to our customers, we recently earned the highest customer service ranking among low-cost carriers by J.D. Power and Associates for the eighth consecutive year.
We're very pleased to be honored with this award along with some of the most respected brands in the world. I'd like to congratulate our crew members for this remarkable achievement and thank them for their continued excellent work in running a safe, reliable operation.
Demand trends remain solid throughout the quarter as we saw strength in all regions. Our year-over-year PRASM growth of 6% exceeded our expectations with strong traffic in the second half of June. During the quarter, East Coast short-haul markets, specifically our business markets from Boston, continued to outperform the rest of our network from a unit revenue growth perspective. We are very pleased with our results in Boston as new markets mature and our share of business traffic increases, resulting in improved profitability.