The net book value of our total lease fleet was $472.0 million at December 31, 2020, as compared to $458.7 million at June 30, 2020. At December 31, 2020, we had 101,251 units (23,656 units in retail operations in Australia, 9,176 units in national account group operations in Australia, 11,944 units in New Zealand, which are considered retail; and 56,475 units in North America) in our lease fleet, as compared to 100,645 units (24,147 units in retail operations in Australia, 8,946 units in national account group operations in Australia, 12,370 units in New Zealand, which are considered retail; and 55,182 units in North America) at June 30, 2020. At those dates, 79,342 units (19,788 units in retail operations in Australia, 8,494 units in national account group operations in Australia, 9,956 units in New Zealand, which are considered retail; and 41,104 units in North America); and 72,983 units (19,505 units in retail operations in Australia, 5,255 units in national account group operations in Australia, 10,149 units in New Zealand, which are considered retail; and 38,074 units in North America) were on lease, respectively.
In the Asia-Pacific area, the lease fleet was comprised of 37,811 storage and freight containers and 6,965 portable building containers at December 31, 2020; and 38,317 storage and freight containers and 7,146 portable building containers at June 30, 2020. At those dates, units on lease were comprised of 33,975 storage and freight containers and 4,263 portable building containers; and 29,839 storage and freight containers and 5,070 portable building containers, respectively.
In North America, the lease fleet was comprised of 40,249 storage containers, 6,679 office containers (GLOs), 4,190 portable liquid storage tank containers, 4,189 mobile offices and 1,168 modular units at December 31, 2020; and 39,169 storage containers, 6,355 office containers (GLOs), 4,194 portable liquid storage tank containers, 4,291 mobile offices and 1,173 modular units at June 30, 2020. At those dates, units on lease were comprised of 29,916 storage containers, 5,410 office containers (GLOs), 1,475 portable liquid storage tank containers, 3,347 mobile offices and 956 modular units; and 27,472 storage containers, 5,184 office containers (GLOs), 1,000 portable liquid storage tank containers, 3,474 mobile offices and 944 modular units, respectively.
Contractual Obligations and Commitments
Our material contractual obligations and commitments consist of outstanding borrowings under our credit facilities discussed above and operating leases for facilities and office equipment. We believe that our contractual obligations have not changed significantly from those included in the Annual Report.
Off-Balance Sheet Arrangements
We do not maintain any off-balance sheet transactions, arrangements, obligations or other relationships with unconsolidated entities or others that are reasonably likely to have a material current or future effect on our financial condition, changes in financial condition, revenues or expenses, results of operations, liquidity, capital expenditures or capital resources.
Seasonality
Although demand from certain customer segments can be seasonal, our operations as a whole are not seasonal to any significant extent. We experience a reduction in sales volumes at Royal Wolf during Australia’s summer holiday break from mid-December to the end of January, followed by February being a short working day month. However, this reduction in sales typically is counterbalanced by increased levels of lease revenues derived from the removals, or moving and storage industry, which experiences its seasonal peak of personnel relocations during this same summer holiday break. Demand from some of Pac-Van’s customers can be seasonal, such as in the construction industry, which tends to increase leasing activity in the first and fourth quarters of our fiscal year; while customers in the retail industry tend to lease more units in the second quarter. Our business at Lone Star and Southern Frac, which has been significantly derived from the oil and gas industry, may decline in our second quarter months of November and December and our third quarter months of January and February, particularly if inclement weather delays, or suspends, customer projects.
Environmental and Safety
Our operations, and the operations of many of our customers, are subject to numerous federal and local laws and regulations governing environmental protection and transportation. These laws regulate such issues as wastewater, storm water and the management, storage and disposal of, or exposure to, hazardous substances. We are not aware of any pending environmental compliance or remediation matters that are reasonably likely to have a material adverse effect on our business, financial position or