At this time, it is uncertain how long our business will be negatively affected by COVID-19 and the associated economic and market downturn.
Second quarter adjusted net revenues of $513.9 million, decreased 4% versus the second quarter of 2019.
For the first six months of 2020, adjusted net revenues of $948.9 million, decreased 1% versus the prior year.
Although our revenues from Investment Banking, that is advisory fees, underwriting fees and commissions, increased by 2% versus the prior period.
Second quarter advisory fees of $336.5 million declined 24%, compared to the second quarter of 2019, which was an unusually strong quarter.
Advisory fees for the six months of 2020 were $695.6 million, a decline of 10%, compared to the prior year period.
We expect our market advisory share -- our market share in advisory fees, among all publicly reported firms, on a trailing 12-month basis to be 8.2%, compared to 8.3% at year-end 2019.
Second quarter underwriting fees of $93.6 million, increased more than 450%, compared to the second quarter of 2019.
For the first six months of the year, underwriting fees were $114.7 million, an increase of more than 160% versus the prior year period.
Commissions and related fees of $54.1 million, increased 11% versus the second quarter of 2019.
For the first six months of 2020, commissions and related fees of $109.5 million, increased 21% versus the prior year period.
Asset management and administration fees from our consolidated businesses were $15.2 million, an increase of 4%, compared to the second quarter of 2019.
For the first six months of 2020, asset management and administration fees from our consolidated businesses were $30.5 million, an increase of 5% from the prior year period.
Turning to expenses, our compensation ratio for the second quarter is 65%, and our compensation ratio for the first six months of 2020 is 63.6%.
A word of explanation about the compensation ratio, the 63.6% accrual in the first half reflects, as it has in past years, an estimate for the full-year compensation ratio, which includes an estimate for 2020 incentive compensation.
The short-term interest being higher earnings this year and the longer-term interest being keeping the team together that has produced more than $2 billion of revenue in 2018 and 2019 and investing in new talent for our future growth.
Non-compensation costs of $77.1 million in the second quarter declined 11% from the second quarter of 2019.
For the first six months, non-compensation costs of $159.9 million, declined 4%.
Adjusted operating income and adjusted net income of $102.7 million and $71.8 million, declined 26% and 29%, respectively, and adjusted earnings per share of $1.53, declined 26%, all versus the second quarter of 2019.
For the first six months of 2020, adjusted operating income, and adjusted net income of $185.3 million and $129.6 million, declined 21% and 29%, respectively, and adjusted earnings per share of $2.74, declined 27% versus the prior six-month period.
Year-to-date, we returned $206 million to shareholders through dividends and repurchase of 1.9 million shares at an average price of $76.22.
Our Board declared a dividend of $0.58, consistent with prior quarters, and reflective of our results for the quarter.
As the quarter began, merger activity was muted as clients managed through the dislocation of the sudden impact of the COVID-19 pandemic.
Announced M&A volumes were down 41% in the first six months of 2020, and the number of announced transactions is down 15%.
The second quarter was particularly weak, announced global M&A volumes were down more than 50%, compared to last year's second quarter and the number of announced transactions declined 29%.
The equity markets are currently strong for many sectors.
We sustained our number one ranking for volume of announced M&A transactions over the last 12 months, both globally and in the US among independent firms.
Among all firms, we are once again number four in the US in announced volume over the last 12 months, and we ranked number three among all firms in the US based on number of transactions for the first six months of 2020.
We were pleased to continue to advise on some of the most important M&A assignments of the first half, including three of the 10 largest global M&A transactions, and four of the five largest M&A transactions in the United States.
We are pleased that we ranked number one among all firms in number of announced restructuring deals and number of completed restructuring deals in the US in the league tables for the first half of the year, and we've been involved in seven of the 10 largest bankruptcies by total actual liabilities year-to-date.
Two recent examples include we were an advisor to Boeing on a $25 billion offering of senior notes, and an advisor to Ford on its $8 billion debt financing.
We served as an active bookrunner or co-manager on six of the 10 largest IPOs in the first half of 2020.
We completed our largest ever active bookrun transaction when we advised PNC on the secondary offering of its 22% stake in BlackRock.
We advised Danaher on its upsized $3.1 billion offering which was split between common stock, and convertible preferred stock.
For the second quarter of 2020, net revenues, net income and earnings per share on a GAAP basis were $507.1 million, $56.4 million, and $1.35, respectively.
For the first half of 2020, net revenues, net income and earnings per share on a GAAP basis were $934 million, $87.6 million, and $2.08, respectively.
For the first half, we expensed $1.1 million related to the Class J LP units.
As we noted last quarter, we expect to incur separation and transition benefits and related costs of approximately $38 million, $8.2 million of which was recorded as special charges in the second quarter of 2020.
Year-to-date, we have recorded $30.3 million as special charges related to the realignment initiative.
Our adjusted results for the quarter and first six months also excluded special charges of $0.4 million and $1.9 million, respectively, related to accelerated depreciation expenses.
Second quarter other revenue increased compared to the prior-year period, primarily as a result of gains of $15.5 million in the investment funds portfolio, which is used as an economic hedge against a portion of our deferred cash compensation program.
Other revenues for the first six months of 2020 decreased versus the prior year, primarily reflecting a net loss of $6.8 million on this investment fund portfolio.
Firmwide non-compensation costs per employee were approximately $43,000 for the second quarter, down 13% on a year-over-year basis.
Our GAAP tax rate for the second quarter was 24.5%, compared to 24.8% in the prior-year period.
On a GAAP basis, the share count was 41.9 million for the second quarter.
Our share count for our adjusted earnings per share was 47 million shares, down versus the prior-year period, driven by share repurchases and a lower average share price.
Finally, with regard to our financial position, we hold $1 billion of cash and cash equivalents, and approximately $100 million in investment securities as of the end of the quarter, as we had transitioned nearly all liquid assets to cash and cash equivalents in the first half.
Our current assets exceed current liabilities by approximately $950 million.

Summary:
At this time, it is uncertain how long our business will be negatively affected by COVID-19 and the associated economic and market downturn.
For the first six months of 2020, asset management and administration fees from our consolidated businesses were $30.5 million, an increase of 5% from the prior year period.
Adjusted operating income and adjusted net income of $102.7 million and $71.8 million, declined 26% and 29%, respectively, and adjusted earnings per share of $1.53, declined 26%, all versus the second quarter of 2019.
Our Board declared a dividend of $0.58, consistent with prior quarters, and reflective of our results for the quarter.
As the quarter began, merger activity was muted as clients managed through the dislocation of the sudden impact of the COVID-19 pandemic.
The equity markets are currently strong for many sectors.
For the second quarter of 2020, net revenues, net income and earnings per share on a GAAP basis were $507.1 million, $56.4 million, and $1.35, respectively.
As we noted last quarter, we expect to incur separation and transition benefits and related costs of approximately $38 million, $8.2 million of which was recorded as special charges in the second quarter of 2020.
Year-to-date, we have recorded $30.3 million as special charges related to the realignment initiative.