Dwayne Hyzak
Analyst · Vernon Plack with BB&T Capital Markets
Thanks, Todd. As Vince and Todd previously mentioned, we are happy to report significant increases in total investment income, net investment income and net asset value for the fourth quarter and year ended December 31, 2011. Total investment income for the fourth quarter and the year increased by approximately 68% for the quarter and 81% for the year over the same period in 2010 to a total of $19.7 million for the quarter and $66.2 million for the year. These increases were primarily driven by increased amounts of interest income associated with higher levels of portfolio debt investments and interest-bearing marketable securities investments, increased dividend activity from portfolio equity investments and increased fee income due to higher levels of transaction activity. The increase in investment income in the fourth quarter also included an increase of approximately $1.1 million of investment income associated with higher levels of accelerated prepayment and repricing activity for certain debt investments.
Fourth quarter 2011 operating expenses, excluding non-cash share-based compensation expense, increased by $2.5 million over prior year to a total of $7.2 million. The operating expense increase was primarily due to higher interest expense as a result of the issuance of $40 million of additional SBIC debentures since December 31, 2010 and increased borrowing activity under our credit facility. The increase also included higher accrued compensation and other operating expenses related to significant increase in investment income and portfolio investment activity compared to the fourth quarter of 2010 and the expenses associated with certain strategic initiatives.
Distributable net investment income for the fourth quarter of 2011 increased by 79% to $12.5 million or $0.48 per share, in comparison to $7 million or $0.36 per share for the same period in the prior year. Our distributable net investment income for the quarter and the year exceeded our dividends paid and resulted in estimated spillover taxable income of approximately $7.9 million or $0.30 per share at December 31, 2011. While the dollar amount of distributable net investment income increased by 79% over the prior year, the per share percentage increase was 33% due to the higher average number of shares outstanding compared to the corresponding period and prior year, primarily due to the impact of the March and October 2011 follow-on stock offerings. All other 2011 per share measures were similarly affected by the higher weighted average shares outstanding.
Distributable net realized income for the fourth quarter of 2011, which included a $900,000 gain on the exit of a portfolio company equity investment, was $13.4 million or $0.51 per share, which represented an increase of $6.4 million or a percentage increase of 191% in comparison to the fourth quarter of 2010. As Vince mentioned, during the fourth quarter of 2011, we recognized $15.2 million of unrealized appreciation in 38 portfolio company investments and $2.8 million of unrealized depreciation in 15 portfolio company investments. The net change and unrealized appreciation for the fourth quarter also included $900,000 of net unrealized appreciation on investments in our marketable securities portfolio, approximately $900,000 of accounting reversals of net unrealized appreciation related to realized gains recognized during the fourth quarter and approximately $600,000 of net unrealized depreciation attributable to our SBIC debentures.
As of year-end, approximately 11.5% of the limited partnership interest of our subsidiary, SBIC Main Street Capital II, were not owned by Main Street. We are happy to report that in the first quarter of 2012, we have completed the acquisition of an additional 8.5% of the limited partnership interest, and we expect to acquire the remaining 3% before the end of the first quarter. These acquisitions are accretive to both net investment income and net asset value, and we believe the elimination of this minority interest provides better clarity in our financial reporting to our shareholders.
Now let me finish with a few portfolio statistics, all as of December 31. In our lower middle market portfolio, we had 54 investments representing approximately $429.1 million of fair value as of year-end or approximately 18.4% above costs. Consistent with our investment strategy, approximately 75% of our lower middle market portfolio investments at cost were in the form of secured debt investments, and approximately 93% of those debt investments held the first lien security position. The weighted average effective yield on our lower middle market portfolio debt investments as of December 31, 2011 was 14.8%. We hold equity positions in 94% of our lower middle market portfolio companies, with an average fully diluted equity ownership position of approximately 34%.
As Vince previously mentioned, at the lower middle market portfolio level, the weighted average net senior debt to EBITDA ratio was 2.2:1 or 2.6:1, including portfolio company debt, which is junior in priority to Main Street's debt position. We expect these portfolio level statistics on a same-store basis should generally continue to improve over time based upon the continued favorable operating performance of our portfolio companies and as our companies naturally delever. In our private placement investments portfolio, we had 27 investments, representing approximately $132.9 million of fair value as of quarter end that we're generating a weighted average yield of approximately 10.6%. Main Street's private placement investments are primarily in the form of debt investments, and approximately 69% of our private placement debt investments at cost held the first lien security position, with most of the remaining investments representing second lien secured investments. Total portfolio fair value as of December 31, 2011 was approximately 113% of the related cost basis, and we had 1 portfolio investment on non-accrual status, representing approximately 0.1% of the portfolio investment at fair value and 1.1% at cost.
Based upon our internal investment rating system, with a rating of 1 being the highest and 5 being the lowest, the weighted average investment rating for our portfolio -- investment portfolio was unchanged from prior quarter at 2.2, and we had 4 portfolio companies improve their rating and no portfolio companies decrease their rating from prior quarter.
With that, I will now turn the call back to the operator so that we may take any questions.