The past 12 months, however, have been anything but normal.
Local and US M&A volume increased 92% and 163% respectively compared to the first half and the number of global and US deals increased 18% and 16% respectively.
And in the US, the largest M&A market for all firms, and for Evercore particularly, M&A volume was down 21%.
Fourth quarter adjusted net revenues of $969.9 million grew 45% year-over-year and full-year adjusted net revenues of $2.33 billion grew 14% compared to 2019, the highest annual revenues in our history.
Fourth quarter advisory fees of $790 million grew 40% year-over-year and full year advisory fees of $1.76 billion grew 6% compared to 2019 and also were the highest in our history.
Based on current consensus estimates and actual results, we expect to maintain our number 4 ranking on advisory fees among all publicly traded investment banking firms and we also expect to grow our market share among these firms.
Importantly, our growth in 2020, combined with declining advisory revenues at the three top bulge bracket firms, resulted in a nearly 50% reduction in the gap between us and the number 3 ranked firm and we narrowed the gap between Evercore and the number 1 and number 2 firms as well.
Fourth quarter underwriting fees of $95 million and full-year underwriting fees of $276.2 million each more than tripled year-over-year.
Fourth quarter commissions and related fees of $52.4 million increased 1% year-over-year and full year commissions and related fees of $205.8 million increased 9% compared to 2019.
Fourth quarter asset administration fees of $20.1 million increased 20% year-over-year and full-year asset management and administration fees of $67.2 million increased 11% compared to 2019.
Turning to expenses, our adjusted compensation rate for the fourth quarter is 52.3% and for the full year is 58.9%.
Fourth quarter non-compensation costs of $85.8 million declined 12% year-over-year.
And full-year non-compensation costs of $316.7 million declined 10% versus [Technical Issues].
Fourth quarter adjusted operating income and adjusted net income of $376.4 million and $277.4 million increased 110% and 113% respectively and adjusted earnings per share of $5.67 increased 108% versus the fourth quarter of 2019.
Full-year operating income and adjusted net income of $639.3 million and $459.6 million increased 28% and 23% respectively and adjusted earnings per share of $9.62 increased 25% versus 2019.
We produced a full-year adjusted operating margin of 27.5%, roughly 300 basis points of margin expansion compared to 2019.
Our Board declared a dividend of $0.61 and we will resume our normal annual reassessment of that dividend in April.
We sustained our number one League Table ranking for volume of announced M&A transactions both globally and in the US among independent firms in 2020 and are advising on 4 of the 10 largest US M&A transactions in 2020.
Our restructuring team ranked number 2 in the League Tables for number of announced US transactions in 2020.
Our restructuring business can deliver service and advice far beyond the traditional Chapter 11 bankruptcy advice and many companies called on us in 2020 for our liability management and financing capabilities.
In 2020, we participated in more than 100 equity and equity-linked transactions that raised nearly $70 billion in total proceeds.
Our team advised on more than $30 billion of deals in GP and LP-led transactions, increased significantly in the second half of the year, and we continue to raise primary capital successfully for these clients.
Finally, our wealth management business grew AUM past the $10 billion mark for the first time in 2020 and provided important investment advice to clients in a challenging environment.
Our continued efforts with the Evercore 100, our program to expand service to targeted large cap nationals and multinationals, our dedicated coverage of financial sponsors and investing in talent to grow in areas of whitespace with the addition of A plus talent will all facilitate our expanded coverage model.
For the fourth quarter of 2020, net revenues, net income and earnings per share on a GAAP basis were $927 million, $220 million and $5.02 respectively.
For the full year, net revenues, net income and earnings per share on a GAAP basis were $2.3 billion, $351 million and $8.22 respectively.
In total, we incurred separation and transition benefits and related costs of approximately $45 million, which reflect a modest increase in the costs from our prior estimate of $43 million.
During the fourth quarter of 2020, we recorded approximately $4 million of special charges, which are excluded from our adjusted results.
There, there is a loss of approximately $31 million for the year included in other revenue that is related to our transition in Mexico.
Our adjusted results for the fourth quarter and full-year 2020 also exclude special charges of $1.3 million and $3.3 million respectively related to accelerated depreciation expense and $1.7 million related to the impairment of assets resulting from the wind down of our Mexico business.
Turning to taxes, our GAAP tax rate for the fourth quarter was 23.2% compared to 21.7% in the prior-year period.
Our GAAP tax rate for the full year was 23.7% compared to 21.2% in the prior period.
And on a GAAP basis, the share count was 43.9 million for the fourth quarter and 42.6 million for the full year.
Our share count for adjusted earnings per share was 48.9 million for the fourth quarter and 47.8 million for the full year.
Firmwide non-compensation costs per employee were approximately $47,000 for the fourth quarter and $172,000 for the full year, each down 9% and 11% on a year-over-year basis respectively.
As of December 31, we held approximately $830 million in cash and cash equivalents and $1.1 billion in investment in securities.
As of December 31, we have made commitments to pay more than $450 million related to future cash payment obligations under our long-term deferred compensation programs and these payment obligations exist at various dates through 2024.

Summary:
Fourth quarter adjusted net revenues of $969.9 million grew 45% year-over-year and full-year adjusted net revenues of $2.33 billion grew 14% compared to 2019, the highest annual revenues in our history.
Fourth quarter adjusted operating income and adjusted net income of $376.4 million and $277.4 million increased 110% and 113% respectively and adjusted earnings per share of $5.67 increased 108% versus the fourth quarter of 2019.
Our Board declared a dividend of $0.61 and we will resume our normal annual reassessment of that dividend in April.
For the fourth quarter of 2020, net revenues, net income and earnings per share on a GAAP basis were $927 million, $220 million and $5.02 respectively.