Caterpillar has announced second quarter 2018 sales and revenues of US$14 ($A18.8) billion, 24% up on the $11.3 billion in the second quarter of 2017.

Of course those figures take in more than just the mining business. In the second quarter Caterpillar's construction business was the sales and revenue leader at $6.2 billion, followed by Energy & Transport at $5.7 billion and then Resource Industries with $2.5 billion.

However, when it comes to profit by segment Resources Industries showed the biggest growth by far year on year. Its second quarter 2018 profit was $411 million, more than four times its $99 million in the second quarter of 2017.

The division's $2.5 billion total sales were an increase of $690 million on the second quarter of 2017, thanks largely to higher demand for equipment across all regions.

Caterpillar says its Resources Industries' order backlog is about flat because increased order rates have been offset by increased production and sales.

Nevertheless Caterpillar dealer WesTrac has taken the step of buying in $100 million equipment in anticipation of customer demand.

That increased demand has been driven by commodity prices remaining strong in the second quarter of 2018, leading customers to invest in current fleets and mine expansions.

However, while there have been increased sales, Caterpillar believes there is more to come because it believes many of its customers have not yet started full-scale fleet replacements.

Operating profit for the second quarter was $2.17 billion, compared to $1.18 billion in the second quarter of 2017. Higher sales volume predominantly drove the $983 million increase.

Manufacturing costs were higher, due to higher freight and materials costs. The higher material costs were mostly due to increasing steel prices.